用加下划线的词语写句子。
他一边放牛,一边找书来读。
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③2F2+2H2O═4HF+O2④2Na+2H2O═2NaOH+H2↑
⑤2Na2O2+2H2O═4NaOH+O2↑ ⑥SiO2+2NaOH═Na2SiO3+H2O
It was not until dark ___ he was aware of ___ he thought was the correct way to solve the problem.