She is in a poor ____f health, which worries her mother much.

--- Can you shoot that bird at the top of the tree?--- No, it's out of ____.

There are certain _______when you have to interrupt people who are in the middle of doing something.

Please speak in a _______ , or the teacher will hear what you say.

A successful scientist needs _____ if he wants to make hypothesis (假设) of how processes work and how events take place.