_______cloning human embryos is not legal in many countries, some scientists are already pushing ahead with research in order to produce a cloned human baby.
| A．While | B．When | C．Since | D．if only |
---Are you going to Tom’s birthday party?
---________．I might have to work．
| A．It depends | B．Thank you | C．Sounds great | D．Don’t mention it |
He had his camera ready ____he saw something that would make a good picture．
| A．even if | B．if only | C．in case | D．so that |
Look over there--- there’s a very long，winding path _____up to the house．
| A．leading | B．leads | C．led | D．to lead |
I'm afraid he’s more of a talker than a doer, which is ____ he never finishes anything．
| A．that | B．when | C．where | D．why |
They are broadening the bridge to ____ the flow of traffic．
| A．put off | B．speed up | C．turn on | D．work out |