求一道SAT语法解答

求一道SAT语法解答
Contrasting with most other fifteenth-century rulers, Portuguese kings could count on the support of the aristocracy in any overseas ventures.
答案是把头上改成Contrasted with. 为什么这里用被动.我在朗文词典上看到这样的例句：The snow was icy and white, contrasting with the brilliant blue sky.他比是自己跟别人比,又不是被比较.
字典里查出来contast作动词有两个意思：
1.使对比,使对照 vt
It is interesting to contrast the two proposals.
2.形成对照 vi
His actions contrast sharply with his promises.
这里我觉得是2，第一，解释的通（用法和上面的例句一样）；第二，它是不及物的。
是2的话，就是主动，就应该是CONTRASTING
求详细解释