553.When do we need to pay the balance?
________ September 30?
A.In
B.By
C.During
D.Within
554.People have always been curious _____ how living thigns on the earth exactly began.
A.in
B.at
C.of
D.about
553.答案是B;by 不迟于，在…之前；the balance 余欠之款。
554.答案是D;be curious about sth.对某事物感到好奇。
