请根据括号中的中文提示或句意，写出句中所缺单词，使句子通顺。
The boy often feels _____________(孤独）when he stays at home alone.
I hear you have been to Hong Kong, can you tell me your e_____________ there?
He ___________(意识到）he was wrong.
We would take action to _____________(减少） the pollution.
The car rushed at high s___________.