SinceWilliamhadbeenseriouslyillforseveralmonths,hisparentswereworriedabout________toreturntoschoolfull-time.

设,其中为任意常数，则下列向量组线性相关的为()

设幂级数的收敛区间为（-2，6），的收敛区间为（）

Thosewho’dliketovisittheexhibition________(sign)yournameshere.

I'msorryIforgottowrite;Ihadsomuchelse________mymind.