请根据括号中的中文提示、英文释义或句意，写出句中所缺单词，使句子通顺。
小题1:Tom is __________ (缺席) from class today. His mum is ill, he has to look after her at home.
小题2:We should pay attention to ________ (grow and improve) a good habit of study.
小题3:I received his invitation yesterday, but I didn’t _________ it because I had something more important to do.
小题4:Our earth is becoming dirtier and dirtier. We should try our best to reduce the __________(the state of being dirty)
小题5:He will write to me as soon as he __________(到达) Paris.