解释下列词语。

①赞赏：                                                  

②承诺：                                                  

③同胞：                                                  

④衷心：                                                  

⑤期待：                                                  

⑥有朋自远方来，不亦乐乎：                                

⑦届时：                                                  

辨析以下说法：①铝合金是用量最大，用途最广的合金  ②袋装食品中可装入硅胶作干燥剂  ③漂白粉的有效成分是次氯酸钙  ④光导纤维的主要原料是硅单质。其中不正确的是

A．②③

B．③④

C．①④

D．②④