问题
选择题
He tried to deal with the increasing burden of his work, but he finally ______ and had to take a complete rest.
[ ]
A. broke off
B. broke away
C. broke out
D broke down
答案
答案：D
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He tried to deal with the increasing burden of his work, but he finally ______ and had to take a complete rest.
[ ]
A. broke off
B. broke away
C. broke out
D broke down
答案：D
代表两种不同元素的原子。这两种元素分别组成的单质在点燃条件下发生反应，反应前后的微观模拟图如下，请回答下列问题。 
，请用A、B表示该反应的化学方程式：_____________。