句子的主语是 raising pets such as dogs and cats in big cities 整个分词短语,当单数看,所以用了is.
pets such as dogs and cats 像猫狗这样的宠物,such as.经常跟着名词之后,表示列举
例如:There are few poets such as Keats and Shelly.像济慈和雪莱这样的诗人现在很少了.
Animals such as rabbits and deer continue to be active all winter,finding food wherever they can .像兔和鹿这样的动物整个冬天都是很活跃的,它们到处寻找食物.