—Must I turn off the gas after cooking?
—Of course, you can never be ____careful with that．
| A．enough | B．very | C．so | D．Too |
A new technique ____ out, the yields (收成) increased by 20% .
| A．having working | B．having been working |
| C．has worked | D．had been worked |
---What do you think of my suggestion?
--- Sorry. What's that? I ____ about something else.
| A．thought | B．am thinking | C．was thinking | D．had thought |
--- Haven't I told you that I like the beef well done?
---Yes, but I _____ it longer than I usually do.
| A．was cooking | B．will cook | C．cooked | D．had cooked |
I haven' t seen Mary these past few days. I m afraid she ____ herself for some time.
| A．isn't feeling | B．hasn' t been feeling |
| C．hadn't been feeling | D．wasn't feeling |
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 |