A、BECAusE it CAn strEngthEn thEir BACk musClEs.
B、BECAusE thEy ArE not CArrying thEir BoDy wEight on thEir FEEt.
C．BECAusE it inCrEAsEs your strEngth morE quiCkly.
D．BECAusE thEy CoulD gEt A littlE out oF BrEAth.