You can use one of the following:
He was told by police that they would try to find his motorbike.
He was told that the police would try to find his motorbike.
Police is treated as plural and usually "the police" but never "a police". If you were to refer to an individual police officer, then it would become an adjective to the noun officer, man or woman e.g.. a police officer; a policeman; a policewoman.
In newspaper headlines, editors tend to leave out as many words as possible for space-economical reasons. It also helps readers to read the headlines very quickly to rouse their interest in reading the rest of the article.
So "A man was robbed while he was sitting at home" becomes:
Man Robbed At Home
Some standard parts of sentences that are left out of headlines are:
- articles (a man -> man)
- auxiliary verbs (a man was slapped -> man slapped)
- copulative "be": (the new major is very happy -> New Major Very Happy)
There are many more, and it can be an interesting exercise to try and reconstruct a complete, correct sentence out of condensed headlines :)
Although a bit of ambiguity is not bad for a headline (it helps attract attention), in this case I do not see ambiguity.
If slapped was meant as an active verb, I would have expected the object to be mentioned - otherwise it makes no sense.
"A man slapped his neighbour" would become "Man Slapped Neighbour", not "Man Slapped Visiting Neighbours House".
For a headline like "Company Sued for Millions", I also see little confusion: if it is the company doing the suing, it is only news while the case is ongoing, so it would be "Company Sues For Millions"
Best Answer
Assume for the moment that "the car" (automobile) was invented at an identifiable time. The word "before" in the test question renders the past perfect tense ("had been invented") unnecessary and verbose.
The short answer is that either "was invented" or "had been invented" is good enough, but "was invented" is possibly better, because of its brevity.
Also for brevity, I would strike "Back in the days," saying, "Before the car was invented, the only personal means of transportation were the horse and the bicycle."
An example of a sentence in which the past perfect is necessary is, "When roller skates were first produced, the automobile had not been invented."