______ life began on earth is one of the biggest puzzles that scientist found hard ______.
A.How; solving | B.When; to be solved |
C.How; to solve | D.Which; to solve |
推荐套卷
______ life began on earth is one of the biggest puzzles that scientist found hard ______.
A.How; solving | B.When; to be solved |
C.How; to solve | D.Which; to solve |