下列各句中，“之”的用法和意义与其他三项不同的是（ ）

Out of the crowded bus ______, who was dressed in a black suit, waving to a woman.

What a lovely toy race car! Could you tell me

________ in looking after three children athome, she no longer has time to enjoy various activities in theclub

After ____ seemed about a quarter, Li Lin managed to work out the difficult math problem, which pleased our teacher.