下列各组转化中,一定条件下均能一步实现的组合是( )
A:①②③
B:①②
C:①③
D:②③
Lao She's Teahouse ______ the changes in Chinese society over fifty years.
图示为儿童蹦极的照片,儿童绑上安全带,在两根弹性绳的牵引下上下运动.在儿童从最高点下降到最低点的过程中( )