People in Switzerland enjoy skiing and【skating】in winter(skate)
答案解析：喜欢做某事：enjoy doing sth (动名词做并列宾语）
It takes Tom 'an hour and a half' to do his homework(对引号部分提问）
【How】【long】does it take Tom to do his homework?
答案解析：对时间长度提问,用how long
There is 'a' letter on the desk.（对引号提问）
【How】【many】【letters】_are there on the desk?
答案解析：多数量提问,用特殊疑问词：+可数名词复数how many +名词复数
I sometimes go to school on foot.（句意不变)
I sometimes【walk】【to】school.
答案解析:go to some place on foot =walk to some place
His ambition is to be an architect(句意不变)
He 【wants】【to】be an architect
答案解析：他的抱负是想成为建筑师,也就他成为建筑师；也就想做某事情=want to do sth；希望做某事情：hope to do sthHis ambition is to be an architect(句意不变)He 【wants】【to】be an architect 答案解析：他的抱负是想成为建筑师，也就他成为建筑师；也就想做某事情=want to do sth；希望做某事情：hope to do sth答案解析：因为时态为一般现在时态，主语为三人称单数，句子谓语动词也需要变单数，所有要加s变为单数如果明白并满意，请立即采纳，谢谢！