Apples are usually sold by ________ weight and eggs are sometimes sold by ________ dozen.
| A．the; the | B．/;a |
| C．/; the | D．the; a |
19. The teacher asked us to write a ________ article.
| A．700 word | B．700-words | C．700’s words | D．700-word |
18. I used to be a very delighted girl. I guess no human being could have passed _______ childhood.
| A．a happy | B．a happier | C．the happier | D．the happiest |
17. The new outline will throw light _______ students’ understanding of history.
| A．upon | B．at | C．of | D．Over |
--- Well, Linda, I’m sorry but I have to leave.
--- _______. I hope to hear from you soon.
| A．So am I | B．Enjoy yourself | C．Don’t be so sad | D．Keep in touch |
15. Researchers _______ to develop vaccines and this will probably take several months to complete.
| A．are working | B．worked | C．will work | D．has worked |