15×5=____   120×7=____

8×12=____   22×4=____

晶体硅是一种重要的非金属材料，制备纯硅的主要步骤如下：

①高温下用碳还原二氧化硅制得粗硅

②粗硅与干燥HCl气体反应制得SiHCl₃：Si+3HClSiHCl₃+H₂

③SiHCl₃与过量H₂在1100℃反应制得纯硅，已知SiHCl₃能与H₂O强烈反应，在空气中易自燃．

请回答下列问题：

听第6段材料，回答小题。

根据句意，用括号内所给单词的适当形式填空。
____ The maths problem is so difficult that few of the students can work it out_______ (easy).
____ Jim is a brave man. He always tells_________ (he) to calm down when he meets trouble.
____ Very few of people believe what the boy says because he is_________ (honest).
____ Everyone was very happy because of the famous writer’s _________ (arrive).
____ In the film, the soldiers were excited when they got their________(wife) letters.