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

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

intense design and development effort ___to the introduction of electronic exchanges.为什么用has been applied不用have been applied?
看我的 这个句子的主语是 effort 所以用单数
design development都是修饰 effort

Automation refers to the introduction of electronic control and automatic probably implies that _. A) wages should be paid on the basis of