The benefits of exercise cannot be stored for long. They should be renewed each day. Astronauts who have spent long periods of time in space know at first hand how weightlessness works to weaken man's muscles. On earth when our muscles lift, push or pull, they work against the resistance of gravity to maintain tone and to build strength. With the removal in space of this resistance, they tend to lose their strength and endurance. That is why the legs of recently returned astronauts feel so wobbly when they first resume the normal task of supporting the body's weight.

Q. Underline the sentence in the paragraph which supports the correct answer to question No. 1.