些 may be used to indicate the plural.
这些是中国人； 那些是英国人； 哪些是美国人？Zhèxiē shi zhōngguórén; nàxiē shi yīngguórén; nǎxiē shi měiguórén? 'These people are Chinese; those people are British; which people are the Americans?'
哪 nǎ is 'which'
There are alternative pronunciations: zhèi, nèi and něi. These are common, for example, in Beijing and sound less formal than zhè, nà and nǎ.