刚也看了这题,sdcar大神解释得很好啊,原文中说了A certain cultivated herb is one of a group of closely related plantsthat thrive in soil with high concentrations of metals that are toxic to mostother plants,所以closely related plants是可以在重金属环境下生长的~,后面这一句thrive...是修饰a group of closely related plants的哦,因为thrive是复数形式的动词~,所以C对咯!