what cause the fire?what do you see just now?

题目

what cause the fire?what do you see just now?
请问 这两句提问为何一句带do,而另一句却不带?与什么有关?都是特殊疑问句吗?

答案

第一句的what充当 句子主语;
第二句what 充当宾语 ,you是主语.