15. The hiding man made a hole in the wall ______ he could observe the outside.
| A．in which | B．by which | C．through which | D．with which |
How beautifully Mary sings! We have never heard _____ voice.
| A．a better | B．a best | C．the better | D．the best |
We must keep our room clean, for dirt and disease go______.
| A．hand in hand | B．step by step | C．from time to time | D．one after another |
The plans flew smoothly ______ in the sky and people spoke ______ of theexperienced pilots.
| A．high；high | B．highly；highly | C．high；highly | D．highly；high |
Thanks to the good care of the nurses ,the boy is ______ recovering from his lung operation .
| A．quietly | B．actually | C．practically | D．gradually |
Mike came late again. It is _____ of him to keep others waiting.
| A．normal | B．ordinary | C．common | D．typical |