单选题：It is not immediately clear ________ the financial crisis wi..

Make full use of your time _____ you can achieve what you desire. [ ]A. so B. or C. butD. and

— Are you good at either math ________ physics?— I'm not good at math, ________ do I do well in physics.[ ] A. or; orB. nor; norC. nor; orD. or; nor

A good idea occurred to Mr. Baker________ to his invention recently. [ ]A. while applyingB. while appliedC. while he was applying himselfD. while applying himself

At school, some students are active ______ some are shy, yet they can be good friends with one another.[ ]A. whileB. althoughC. so D. as

I would appreciate it________you call back this afternoon for the doctor’s appointment.[ ]A．untilB．ifC．whenD．that