Please help with the correct Ans.

The new medicine has helped many people feel better since it ____ last year.

(A) was introduced

(B) introduced

(C) has introduced

(D) was introducing

Since + PP (Option C ) and option D has been ruled out obviously.

I am confused between A and B. think the ans should be "Introduced" as Since can't be followed by "was introduced". the sentence does not look like a reported speech.

Please help with the correct ans.

Is there any link which will tell us the correct usage of "Since" with different verb forms i.e. Since should or should not be followed by what and what. This will be of real help.