DNA is very useful for us, it many years ago. (1.0)
A: discovers
B: discovered
C: is discovered
D: was discovered
A: discovers
B: discovered
C: is discovered
D: was discovered
举一反三
- It ______ long ago that the earth is round. A: was discovered B: is discovered C: discovers D: discovered
- He became very friendly when he ____________ that she was my sister. A: was discovered B: discovers C: has discovered D: discovered
- Advertisers discovered years ago and all of us love to get something for nothing.
- The scientist ________ a new bacteria in 1912. A: discovered B: was discovering C: discovers D: have discovered
- Then I discovered,______ was news to me,that this girl is the very one I helped years ago. A: that B: why C: what D: how