The primary impulse of each human being is to（）himself, but the secondary impulse is to venture out of the self, to correct its provincialism and heal its loneliness.

Current estimates put thirteen percent of global flora ...

单项选择题Current estimates put thirteen percent of global flora at risk of extinction, but this number does not include （） plants from tropical regions, where the majority of the world's plants grow.

The teacher has （） catering to some students, but to re...

单项选择题The teacher has （） catering to some students, but to retain his tenure, which effects only after a teacher has unanimously gratified his students, he offers his complaints （）.

Although scientists have long （） the human appendix as ...

单项选择题Although scientists have long （） the human appendix as （）organ, there is a growing body of evidence indicating that the appendix does in fact have a significant function as a part of the body's immune system.