But taking a cue from health experts, a group of 19 restaurant companies are pledging to offer more-healthful menu options for children at a time when concern is growing over the role of fast food in childhood obesity
这是12年四级题 有一个地方不太懂 为什么but 后面 要用taking 而不是take，我的理解是 整个句子有两个连词but和when所以要有三个谓语动词，已经有了is和are 所以要用take 求解答