用方框中所给单词的适当形式填空，每词限用一次。            

(1) Take some rest after lunch and you won't feel ____ in the afternoon. .

(2)When the child saw her parents waiting at the school gate, she ran ____  them.
(3)Don't ____  about your exams, everything will be fine.
(4)To protect____ , scientists suggest the people stop fishing in some parts of the ocean.
(5)My host family is really nice .They try____  best to make me feel at home .

小智因皮肤黝黑，有同学给他起了个“黑炭头”的外号，并且在同学中散播。其他同学一见到小智都叫他“黑炭头”，小智的心里很不好受。

在收音机线路中，经天线接收到的电信号既有高频成分又有低频成分，经放大后送给下一级，需要把低频成分和高频成分分开，只让低频成分输入给下一级，我们采用了如图装置电路，其中代号a、b应选择的元件是(　　)