1.That在从句中要做成分的,而这一题的从句she works as a nurse句子完整,不缺主谓宾,hospital是地点,in a hospital是地点状语,所以用where
2.因为这里do是及物动词,后面要带宾语.如果要用we should do应该用what we should do,如果用how we should do的话do后面要加一个it.
3.答案是because吗?我觉得应该用because of更合适.because后面要接从句,because of后接名词.而the heavy snow是名词短语,所以用because of.
4.take care of的意思是照顾、照看.look out for是注意、小心的意思.与look out for意思相近的短语是be care of,不是take care of.