did you know _______?A what they happend?B what happend to them?这两个答案我很不确定,哪一个是正确的?

did you know _______?A what they happend?B what happend to them?这两个答案我很不确定,哪一个是正确的?
did you know _______?A what they happend?B what happend to them?
这两个答案我很不确定,哪一个是正确的?

did you know _______?A what they happend?B what happend to them?这两个答案我很不确定,哪一个是正确的?
Did you know what happened to them?

might be B is right...

选B，know后面是宾语，they不对