I can remember very few ______ when he had to cancel his plans because of poor health.

Mr．Barret doesn’t think that all bad language should be allowed．In his opinion, there are _____ that should be kept up．

The doctor finally gave up the ____ of medicine for full - time writing．

The advice is of great ________ to our work. We all think it ________.

Parts of the cave have been badly affected by rain and           to the air.