单项选择题
His argument does not suggest that mankind can ________ to be wasteful in the utilization of these resources.
单项选择题 Your father likes to play golf; he's really enthusiastic ________ it.
单项选择题 The tour of our country by the foreign visitors ________ on the workings of democracy.
单项选择题 Without the friction between their feet and the ground, people would ________ be able to walk.
