One of the real services of the historical novel is not that it can be a substitute for history, but that it can be a(n) extension.()

单项选择题A corps of so-called barefoot doctors are trained in hygiene, preventive medicine, acupuncture, and routine treatment of common diseases.()

A．nutrition
B．sanitation
C．nursery
D．welfare

单项选择题His inability to learn foreign languages was a(n) obstacle to his career.()

A．barrier
B．excess
C．carrier
D．impulse