---__________ is the most difficult of all the lessons.

--- I agree. But it’s the most interesting.

A．Lesson Three

B．Lesson Third,

C．The Three Lesson

D．Third Lesson

下列对角焊缝的构造要求，正确的是()。

①角焊缝的焊脚尺寸hf≥1.5(t为较厚焊件的厚度);

②角焊缝的焊脚尺寸hf≤1.2t(t为较薄焊件的厚度);

③侧面角焊缝或正面角焊缝的计算长度不得小于8hf，或40mm;

④侧面角焊缝的计算长度不宜大于40hf。应该是60hf

A.①②

B.①②③

C.①②③④

D.①③④