______ a pair of compasses, it is easy to describe a circle.

Please arrange ___ first, and then let him have a good rest.

Science and technology are developing ______ quickly that some new electronic products are out-of-date within several months. 

Only when you told me about it ________ what a silly thing I had done.

— Do remember to take this medicine three times a day with warm boiled water. — _________.