Thedestructionofthetwintowers_________shockandangerthroughouttheworld．

设数列 {an} 的前 n 项和为 Sn，则 {an} 等差。

(1) S n4=n 2+2n, n=1,2,3

(2) S n4=n 2+ 2n +1,n=1,2,3

Thepoorcountriesareextremely_______tointernationaleconomicfluctuations

John says that his present job does not provide him with enough ______for his organizing ability.

Allherhardwork__________intheend，andshefinallypassedtheexam．