问题
单项选择题
A. Experts in the medical field have doubled in the past five years.
B. Both health food and medical authorities have recommended Vitamin E.
C. The health food experts are not authorized to comment on Vitamin E.
D. The selling of Vitamin E must be approved by the leading medical authorities.
答案
参考答案：B
解析：
The sales of Vitamin E, helped by the testimony of health food experts and a number of leading medical authorities, have doubled in the past five years.