1 . He _____ his potential had it not been for his desire to meet new challenges.

A．would never have realized	B．would never realize
C．never realized	D．had never realized

2 . I didn’t know he was in the company. _______it, I_______then.

A．Had I known; would call on him

B．Should I know; would have called on him

C．If I knew; would call on him

D．Had I known; would have called on him

3 . ____ then what I know now, I would have made different decisions.

A．Should I know

B．I knew

C．I did know

D．Had I known

4 . What a pity! The parents could have survived the earthquake, __________ to save their child.

A．had they not come back	B．have they come back
C．did they not come back	D．did they come back

5 . It might have saved me some trouble      the schedule but unforgettably no one told me about it.

A．did I know

B．have I known

C．do I know

D．had I known

6 . ---It's a complete pity that you missed the wonderful lecture.
---Terribly sorry! _____my former colleague not come to me unexpectedly.

A．Should

B．Would

C．Had

D．Did

7 . You could come back by Friday ________ today, which can ensure your presence at my birthday party.

A．should you start off	B．did you start off
C．had you started off	D．would you start off

8 . This car is important to our family. We would repair it at our expense _______ it break down within the first year.

A．could	B．would
C．might	D．should

9 . “It might have saved me a lot of money”, Mr. Chen sighed, “________ timely from the stock market this July”.

A．did I withdraw	B．should I withdraw
C．have I withdrawn	D．had I withdrawn

10 . The bus would not have run into the river ________ for the bad tempered lady.

A．if it were not	B．had it not been
C．if it would not be	D．should it not be