Knowing _____, as a matter of fact, one shouldn’t know is a terrible thing．

My sister will never speak to others like that ________they say something unpleasant to her .

As many as five courses are provided, and you are free to choose ______ suits you best.

 ________ you have to do the job, you should try your best to do it well even though it may be very difficult for you.

I was so familiar with her that I recognized her voice       I picked up the phone.