I thought it was __________ to donate money to this fund.

 Looking at my mother's ___________ face, I regretted not having told her my whereabouts on the phone.

Hearing the loud noise，the boy looked out of the window,__________.

Mary once taught English in a remote village school as a volunteer, which is ________ only on foot.

 Polar explorers have to be extremely _____ to bear the climate and other hardships.