Which of the following sentences is grammatically INCORRECT？A．Bookings is obtainable from

Which of the following sentences is grammatically INCORRECT？

A．Bookings is obtainable from travel agents.

B．Diabetes is a common disease.

C．The scissors are dull.

D．The militia were called out to guard the borderland.

请帮忙给出正确答案和分析，谢谢！