Similarity作“当类似;相似”讲,是不可数名词；作“相似点;类似点”讲,是可数名词。
There was a very basic similarity in our philosophy
我们的人生哲学在根本上很相似。
There were significant similarities between mother and son
母子之间有很多相像的地方。
The similarities between Mars and Earth were enough to keep alive hopes of some form ofMartian life.
火星和地球之间的诸多相似处足以让人们对火星上存在某种生物抱以希望。