intense design and development effort ___to the introduction of e_英语解答

intense design and development effort ___to the introduction of electronic exchanges.
为什么用has been applied不用have been applied?

人气：115 ℃　时间：2020-04-01 17:08:34

解答

看我的这个句子的主语是 effort 所以用单数
design development都是修饰 effort