用系动词翻译句子
【小题1】How he managed to get out of the house without being seen ____________________（对我们来说仍是一个谜）.
【小题2】____________________（那位老人睡着了）when he was watching TV alone.
【小题3】His wish to ____________________（成为一名科学家）one day ____________________（终于实现了）.
【小题4】____________________（她尽量显得镇定）even when she felt worried inside.
【小题5】____________________（树上的叶子变绿了）when spring comes, which makes a beautiful scene.