— The woman biologist stayed in Africa studying wild animals for 13 years before she returned. — Oh, dear ! She ______ a lot of difficulties !
But for friction (摩擦力), people ______ neither walk, nor even stand up.
It was after he got what he had desired_____ he realized it was not so important.
He was allowed to go swimming _______ he kept near the other boys.
Since he often travels on business, he can ______ himself to sleeping in any place he can find.
_____ took me almost 20 years to have the courage to ask my father this personal question.