“有之必然无之未必不然”形容的是哪种逻辑关系？（）
A、必要条件
B、充分条件
C、充要条件
D、以上都不是
参考答案：B
—What can we do to improve the environment of Beijing?
—More and more trees _______, I think. [ ]
A. must be planted
B. must planted
C. must be plant
D. must plant
物价上涨就是通货膨胀（）。
