31．—Can I smoke here?
—No．On no condition ______ in the museum．
| A．is smoking permitted | B．smoking is permitted |
| C．was smoking permitted | D．smoking was permitted |
— Do you know the old man ______ on the bench over there?
— He is my grandfather.
| A．sit | B．sat | C．to sit | D．sitting |
If you don’t learn to think _____ you are young, you may never learn.
| A．when | B．where | C．what | D．which |
A new way of teaching _____ in the article can make learning easier.
| A．introduced | B．has introduced | C．was introduced | D．is being introduced |
My mother asked me where _____, and I told her that I was going to buy some food.
| A．I am going | B．am I going | C．I was going | D．was I going |
I still don’t know ______ she’s planning to come to my birthday party or not.
| A．whether | B．when | C．why | D．that |