It’s necessary for you to _____ at least an hour each day to learn the new vocabulary.

He is ill. I don’t know _______ he will come to school.

下列各句中，加线的成语使用恰当的一项是（ ）

He is really considering _____ himself to ______ these children of the poor mountain village.

ter studied hard at school when she was young, which contributes ________ her success in her career.