Teenagers __________ their health because they play computer games too much.
| A．have damaged | B．are damaging |
| C．damaged | D．will damage |
Eric received training in computer for one year, _______ he found a job in a big company.
| A．after that | B．after it | C．after which | D．after this |
With the help of high technology, many new substances（物质）______in the past years.
| A．discovered | B．have discovered | C．had been discovered | D．have been discovered |
______ is know to us all, good friends ______ happiness and value to our life.
| A．It; add | B．As; add up | C．It; add up | D．As; add |
Letterboxes are mu
ch more _______ in the UK than in the US, where most people have a mailbox instead.
| A．common | B．ordinary | C．normal | D．usual |
I’m certain David’s told you his business trouble. ________, it’s no secret that he owes a lot of money to the bank..
| A．However | B．Anyway | C．Therefore | D．Though |