Proper exercise plays a significant role in the rehabilitation of patients with various back ailments.

单项选择题The polar regions are generally covered with ice and snow.

单项选择题It is not possible for people to remember everthing that they have thought.

单项选择题A fossil is a remnant of a once-living organism.

单项选择题In temperate regions the growth rings on turtles’ epidermal plates reflect seasonal variations in growth.