很高兴为您解答如下：
1、【B】from Beijing to Paris!
A how long way it is B what a long way it is C how long way is it D what long way it is
感叹句型：what （+冠词a/an) +形容词+名词+主谓； how + 形容词 + 主谓,可排除AC,另外way“路径”是可数名词,所以需要加冠词a
2、【D】letters there are in his desk!
A how many B How very many the C what so many Dwhat many
由there are前的letters可排除how的AB,另外,有what不需要副词so,若没有what,可以用so.
3、The hospital where my mother works was built last year.
【可以】The hospital my mother works in was built last year.或者The hospital in which my mother works was built last year.
定语从句引导词in which表地点时=where,把in放在句中时,引导词用which,可省略.
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