system 這個英文字 有冇plural 即 systems

有

Singular form, e.g.
- a system (e.g. an eco-system; a system of networks)

Plural form, e.g.
- two systems (as in " One country, two systems ")
- An analysis of the different systems in place.

In addition, " systems " can be used as an adjective as follows:
- a systems analyst (a kind of professionals whose work is to analyse the logic of programming in the development of computer programs)

Hope the above helps.

有

單數: system
複數: systems

wiki: http://en.wikipedia.org/wiki/System