1 is b (about the apple)
2 could be a or b (about the medications) Perhaps the medications are to be taken only if necessary at the discretion of the person taking them.
3 is not a correct sentence. It is ambiguous and extremely unclear. Also, the second "it" is unnecessary and repetitious.
Last edited by tigerpaws; 18-Jun-2009 at 05:53.
Reason: corrected my spelling
a-It is for us to act.
b-It is for you to decide whether you want to stay or leave.
c-It is for him to defend his honor.
I think my sentence 3 was confusing, especially since it had no context. This structure is not incorrect.... At least I don't think it is...My apologies for picking an awkward example, or for being hard-headed, as the case may be!
b and c are fine. "a" sounds either very dramatic or like a poetic way to express something. More clearly one might say: We must act! Less formally it would be common to say: We need to do something. or We need to do something about this.