After describing the planned improvements， she went on _____ how much they would cost.

A．to explain

B．explaining

C．to be explaining

D．having explained

烤烟地膜覆盖栽培，掌握最佳盖膜时机的原则是：（）。

A.寒冷地区移栽后盖膜

B.温暖地区提前盖膜

C.多雨地区移栽时盖膜

D.干旱地区趁墒盖膜