He can't collect his thoughts(collect为什么不加s)

His hobby is (to collect) coins.为什么用to collect? collect collect stamp后要不要加s he can't speak english .为什么speak不加s We can collect leaves. what can you collect collect one's 急 collecting stamp这个词组的collect为什么加ing he is like his father 为什么like不加s he is like his father.为什么like不加s He spends as much money as he can _______(collect) stamps His hobby is ____(collect) stamps