单选题 Costs for regulation of business actually are a hidden tax severely reducing the competitive ness of domestic businesses ______ when they face an increasingly global marketplace.

A、 on occasions
B、 at a time
C、 under the circumstances
D、 at once

【正确答案】 B

【答案解析】句意：商务规章实际上是一种隐性税收，面临国际市场时，它严重降低了国内商务的竞争力。at a time某时。