Experiments of this kind _______ in both the U.S. and Europe well before the Second World War.（2011北京卷21）
| A．have conducted |
| B．have been conducted |
| C．had conducted |
| D．had been conducted |
But for electricity, human life _____ so easy today.
| A．isn’t | B．would not be | C．will not be | D．would not have been |
We ___ to start our own business, but we never had enough money.
| A．have hoped | B．had hoped | C．would hope | D．should hope |
—We could have walked to the doctor’s; it was so near.
—Yes. A ride ___ at all necessary.
| A．wasn’t | B．hadn’t been | C．wouldn’t be | D．won’t be |
— Are you going to the ball tonight? —It’s too late now. How I wish ___ about it earlier.
| A．I’ll know | B．I’ve known | C．I know | D．I’d known |
_____ the fog, you would find the beautiful tower in the distance easily.
| A．Had it not been for | B．I at were not |
| C．If it had not been for | D．Were it not for |