If their mother noticed that they have been talking for a long time then it is preferable to use "that much."
But if she just noticed that they are talking then I think she will use "so much."
And in your sentence she said "Don't" which is an order so using "so" is better.
If she used "shouldn't" then "that much" would be better. I think that both are correct, but "so" is more accurate.
"Once a day" and "every" can sometimes be interchangeable. It all depends on context. There are times when using both together might add some needed clarification, but other times when it is unnecessary.
For example, if your Doctor gave you 14 days' worth of medication and told you to take it "once a day", it ought to be obvious that he means once every day until the course of 14 days has run. There is no need to add "every". On the other hand, if someone said "I have to take this medication every day" that could mean they have to take it for the rest of their life.
Similarly, if someone said "I work every day", that might not mean literally every day of the week, year after year without a break. It might just mean every usual work day - such as Monday to Friday - and they just mean to distinguish themselves from a part-time worker who only works some of the usual 'full-time' working week.
In your example, "online security" could be someone's line of work. They may think about it every work day, but not every day without exception. Personally, I don't think the option has been written this way so as to exclusively mean 7 days a week as opposed to 5, but I think it may have been written that way to avoid all of the ambiguity I have just discussed. Interpret it how you want.
Just on a general note, I've seen your various posts picking apart these kinds of multiple-choice survey options. To be honest, you may be seriously over-thinking them. The options don't always make sense to us as native speakers anyway. For example, terms like "strongly agree" and "strongly disagree" are often used alongside "agree" and "disagree", which doesn't stand up to scrutiny. One either agrees wholly, or does not. Survey writers tend to settle on a scale for the answers and then apply that scale to a set of questions for consistency, but without any thought for grammar.
Best Answer
It’s not necessary, but I’m not sure I’d label it as redundant.
I looked up redundant in a dictionary (NOAD), and found this definition:
In English, many words can be omitted without a loss of meaning, but sometimes words are added for emphasis. Calling a word “redundant” makes it sound like it should be removed, and I’m not sure that applies to all superfluous words. (For example, if I say, “The room was very spacious,” is the word very redundant?)
Incidentally, the same dictionary defines the idiom once again as meaning “one more time,” so, in that regard, your sentence works fine grammatically. However, there’s an equivalent idiom that means the same thing – once more:
Personally, if it were me talking, I’d probably use one of these variants:
but I don’t find your original version with once again either particularly jarring or annoyingly redundant.