Question

by the time he__(be) twenty years old,he _(have)20 inventions.咋做

Answer 1

was ,had had.
到他二十岁的时候，他已经拥有20项发明了。
现在20岁已经是过去的事情了，所以用过去式。
而拥有20项发明是在20岁之前，那么就是过去的过去，所以用过去完成。
希望能帮到你.....望采纳....谢谢....

Answer 2

By the time he was 20 years old, he had had 20 inventions.
他20岁之前就已经取得20项专利发明了。
过去完成时态

Answer 3

was
hah had