A:收缩→舒张,收缩→舒张
B:舒张→收缩,收缩→舒张
C:收缩→舒张,舒张→收缩
D:舒张→收缩,舒张→收缩
①光合作用②细胞呼吸③消化吸收④主动运输.
That's the very way he suggests ____ the math problem.