In buses, all of us _________ thieves.
| A．keep an eye out for | B．are keep an eye out for |
| C．are kept an out for | D．keep eye out for |
. So many uses have been discovered for this wood ____ the supply of white pine is becoming smaller and smaller.
| A．then | B．what | C．that | D．which |
The truth, Sir, is that the old man____ across the street when my car hit him.
| A．was to walk | B．had been walking | C．walked | D．was walking |
. ---Where will you start your work after graduation?
---Mmm, it's not been decided yet. I ____ continue my study for a higher degree.
| A．need | B．must | C．would | D．might |
. I wrote to my parents once a week,____ I was too busy with my teaching work.
| A．it | B．unless | C．when | D．as |
. However, at times this balance in nature is disturbed, ____ a number of possibly unforeseen effects.
| A．lying in | B．calling in | C．taking in | D．resulting in |