(That) the sun (but) not the earth (is) the center of our planetary system (was) a difficult concept to grasp in the Middle Ages.

单项选择题The growth (of) part-time and flexible working patterns (allow) more women (to) (take) advantage of employment opportunities.

单项选择题I regret (to spend) (so) much money (on) a car (that) I hardly drive in everyday life.