Parents should pay attention to areas _______ their child is having difficulty and spend extra time to help him or her master those skills.
A．as B．where C．why D．when
We apologize for any inconvenience you _______ have been caused by the delay of the flight.
A．may B．would C．must D．need
The police say there is a $50,000 _______ for any information that helps them find the killer.
A．income B．fee C．bill D．reward
Most whales must come up for air after several minutes, _______ a few can stay under water for an hour or more.
A．while B．or C．for D．so
The numbers that researchers get from the experiments can be _______, just like number puzzles.
A．disappointing B．inspiring C．worrying D．confusing
_______ the house is empty, memories flood my mind of a time when it was filled with life.
A．Since B．Unless C．As if D．Even though
