I'm aware that basic Chinese grammar tends to lack distinction between the plural and singular forms of many nouns. For example,
我的朋友是中国人 could either mean "my friend is Chinese" (singular) or "my friends are Chinese" (plural).
While there could obviously be cultural reasons why the differences between these two sentences mightn't matter, what if they do? If the number of friends is known, could one simply put
三个, etc. in front of
朋友, or is there a better, less kludgy way to do this? What if there's an unknown (but plural) number of friends?
In short, what are some of the best ways to indicate or emphasize the plurality or singularity of nouns in ambiguous cases such as these?