1: No one knows how long it will last. 2: were curious to find out what had happened.
问题描述：
1: No one knows how long it will last. 2: were curious to find out what had happened.
请问第一个句子里的疑问词how long在句中是作know的宾语吗?
第二个句子里的疑问词what是作happen的主语吗?
答
第一句中how long引导的句子（how long it will last ）整个做knows的宾语,并非仅疑问词how long在句中是作know的宾语.
第二句中what had happened这个从句做find out 的宾语,what 是从句中happen的主语,你的判断正确.那么在how long it will last中,how long 作什么?last“持续” 不及物动词（vi.），故how long不可能充当其宾语，只能做状语了。