根据首字母及汉语提示，完成下列单词的拼写，使句意明确，语言通顺。

小题1:The Internet is becoming a u _____ (有用的)tool for students.

小题2:We feel it is our d _____ (责任)to help each other.

小题3:You are b _____ (勇敢的) enough to accept such a difficult job.

小题4:I'm afraid we have to c _____ ( 取消)the meeting.

小题5:Bob has many story books and he often s _____ (分享)thcm with his friends

比较直接插入排序、起泡排序、简单选择排序、快速排序、堆排序、2一路归并排序和基数排序的算法性能，并填写下表：

（28）处填（）。

A．O(n²)

B．O(n)

C．O(1)

D．O(nlogn)

E．O(dn)