根据中文写出单词的适当形式。（5分）

小题1:Even though he is the top student in our class, he is very ________ (谦虚的).

小题2:He is very __________（心灵手巧的）, and he is good at making cards.

小题3:Please give up ________ (争论) about the problem. It’s meaningless.

小题4:It is silly of you not to forgive others for their _______（过错）.

小题5:He didn’t answer your question ________（大概，或许）because he didn’t know the answer.

IP数据报的报文格式如图5-2所示。在没有选项和填充的情况下，报头长度域的值为______ 。

A．3

B．5

C．10

D．20

图5-2 IP数据报的报文格式