Are you an American? Was the test written by a Brit/Red Hater? Examples 1, 2 and 4 are very much the distinction between the BrE and AmE. BrE (words protected) normally makes colons not present. When two independent clauses are conjoined, the comma is used.

In answering the 3rd question, though I don’t suppose it would have been amongst the answer options, also correct, in my opinion would have been:

These rings spread over hundreds of thousands of miles and consist of billions of individual particles…

No pronoun or comma.

“The answer you cite appears to be inconsistent and idiosyncratic. Article A: It appears the examiner has a

• rule that a conjunction is required to join two
• independent clauses and a comma does not precede

this conjunction but then adds

• to it unless that conjunction precedes a pronoun referring to the first clause.

What are some of the best examples of “best behaviour”?