imo E

I think it is C

Please post the correct answers too.

Yes it is C, can you explain?

IMO: B

IMO is C

interval between comet's passes close to earth describes the intervals best

Explaination

Of passing is incorrect usage take off B and D

as it passes means orbit changes when it passes earth which is not what sentene means eliminate E

to use between u need to compare ...something

here between its passes says between forst and second pass...so thar correct, answer C

between passing is incorrect coz of above reason....

The way I saw it was, during always need a between

Explanation ( taken from Spidey's notes )

during + time period is WRONG. For example:
During two hours, I felt sleepy.
but
During the last two hours, I have felt sleepy.
To make our sentence correct with "during," we'd need to add some information that
would identify which two decade-period we are talking about.

hence, between is need narrowing our choices down to A and C. Passing seems wrong - I followed what "gmatinjuly" wrote above ( 1st pass, 2nd pass etc)