Whether you live to eat or eat to live, food is a major _________ in every family’s budget.

单项选择题Now a paper in Science argues that organic chemicals in the rock come mostly from _________ on earth rather than bacteria on Mars.

单项选择题There is much I enjoy about the changing seasons, but my favorite time is the _________ from fall to winter.

单项选择题There is supposed to be a safety _________ which makes it impossible for trains to collide.

单项选择题After four years in the same job his enthusiasm finally _________.

单项选择题No one can function properly if they are _________ of adequate sleep.