--- Oh, Jack’s not here these days. Is he ill?

---________. His mother told me that he was in hospital.

A．I’m afraid so.

B．I hope not.

C．I don’t mind

D．I don’t think so

低碳钢材料在拉伸实验过程中，不发生明显的塑性变形时，承受的最大应力应当小于的数值是（）

A.比例极限

B.屈服极限

C.强度极限

D.许用应力