dinosaurs have been completely died out on the earth,never (being seen) again.
为什么不可以直接用 seen
With a report ( to write )about the accident,I have to find some witnesses for help.
为什么不是 written
It's likely that he is the only American hip-hop artist ( to have ever lived) in China.
为什么不是 having ever lived、、、
About 3100 chinese citizens ( stuck ) in Thailand had returned by Dec.3rd.
having been stuck 的用法错在哪里~(>_