As Vitaly mentioned, this is a ligature: two letters are connected as if written without lifting the pen off the paper.
Ligatures were very common in the Middle Ages, and probably in Antiquity as well. Often the shape of a ligature changed away from its constituent letters with time, so as to render them unrecognisable in some cases. There were thousands of ligatures and abbreviations. Because ligatures usually take a bit less space than full letters, they were a means to save (expensive) paper; and the fact that scribes did not need to lift their pens off the paper as often saved time.
Ligatures are of course much less useful in print. Only some minor economy of space might conceivably be attained; the reason why some ligatures made it into print from time to time is probably tradition.
Generally there was no difference in meaning between ligature and full writing. It is true that certain ligatures are used much more often in one word than in another; the ligature &, which stood for et, was extremely common in the Latin word et ("and"), but significantly less so in other words, though it could be used in any word, such as car&. Nevertheless, this ligature came to be associated with the word et so much that it carried over into other languages, even though the full word would be entirely different, like English and.
The ct ligature is quite natural in Medieval script; I have never seen it used with a specific meaning, and it cannot stand for an entire word on itself. That is why I believe it is applied mostly at random, i.e. it depends on the scribe.
Even so, it is possible that certain printers had specific conventions when to use it; these are unknown to me, and I bet nearly all readers wouldn't know the reason behind such conventions either, if such existed.
If you're interested in Medieval ligatures, you might like to browse Cappelli's dictionary of Latin abbreviations (or its English translation). Some of the Latin ligatures stood for letter combinations that were also useful in other languages and were often so used. Each language also developed some abbreviations and ligatures of its own, but the Latin ones were always the basis. Here is a page displaying the et ligature:
Here is a page of Latin manuscript, where you can see how many ligatures and abbreviations they used:
Nearly every mark or line indicates that something is left out or abbreviated. However, notice that this scribe didn't use the ct ligature, for no apparent reason; such variation is mostly arbitrary and depends on the scribe and his teachers.
English capitalization is a can of worms nestled inside the larger swamp of English spelling -- i.e, there is almost never any good reason for why anything is spelled, punctuated, or capitalized any particular way -- they just are. Sometimes.
However, one contributing reason for this particular feature is probably the fact that both I and O are usually stressed (as one can tell from the fact that they contain diphthongs, which require stress to avoid reduction), while a is never stressed and therefore always reduced to /ə/.
Best Answer
It's all about the subject. As pointed out by Ben Walker, you have actually given us two sentences with the same issue. What helps is to simplify the sentence to subject and verb, removing phrasing. "Which of the sentences is/are grammatically correct?" Which is the subject. A trick an English teacher taught me is to say "which [one]...?" This helps you see that your subject is singular and thus, you would use a singular verb (e.g., "is").
We use "one" because what you are choosing between are two singular items. If, however, you were choosing plural items, such as which M&M colors you wish to eat, your sentence structure would be plural. Using above trick, the question "Which M&M colors are you going to eat?" is "Which [ones] are you going to eat?"
Another little trick that can be helpful is to read the subject and verb aloud. "Which is...?" or "Which are...?" Stilll unsure, say outloud, "Which [one] is...?" or "Which [one] are...?" "One" is singular, so you use the singular verb "is". Or "Which [ones] is...?" or "Which [ones] are...?" "Ones" is plural, so you use the plural verb "are".
Same principle applies to the "Being egocentric and selfish..." sentences. Here, "egocentric" and "selfish" are each singular items combined together as a single unit (i.e., singular). So instead of reading it as "Being [blank and blank]", read it as "Being [blank]". Read aloud, "Being [blank] is dangerous...", "Being [blank] are dangerous..." The answer is "Being [blank] is dangerous." Singular subject uses a singular verb.
Whew, this is my first answer. Seeing the length of it, I do believe I need to work on how to clearly summarize a shorter answer! But I do hope something from the answer above may be of use to you.