I searched for my wallet and it wasn't there. At first, I thought I _______ it at home. Then I remembered _______ it out to pay for the taxi.

A．must have left；to take

B．may leave；taking

C．might leave； to take

D．could have left；taking

向紫色石蕊溶液中通入CO₂，溶液变为______色，反应的方程式______，加热后溶液呈______色，反应的方程式______；长时间盛放石灰水的试剂瓶壁，有一层白色硬膜生成，用化学方程式表示该膜的形成：______．