【单选题】What does the author mean by saying 'we are encouraged to hop when we have two perfectly good legs' (Para. 4) ?
A.
We needn't hop because we are healthy.
B.
Only those who have something wrong in their legs can be encouraged to hop.
C.
It's foolish of us to hop when we have two perfectly good legs.
D.
We should use both sides of the brain.