求高人指点

LSAT22-3-12

One year ago a local government initiated an antismoking advertising campaign in local newspapers， which it finnaiced by imposing a tax on cigarattes of 20 cents per pack。One year later， the number of people in the locality who smoke cigarettes had declined by 3 percent。 Clearly， what was said in the advertisement had an effect， although a small one， on the number of people in the locality who smoke cigarettes。

Which of the following if true helpse to strengthen the argument？

（D）Merchants in the locailty responded to the local tax by reducing the price at which they sold the cigarattes by 20 percents per pack。

不明白这一答案为何加强了作者的论证？？