I answered "alguno," but apparently the answer is "algunos." I don't understand why based on this quote from the lesson. Thanks!
"Sometimes, when alguno and alguna are used in affirmative sentences, it has the nuance of "some random something/someone", "one or two" or "the odd one". The idea is non-specific in number and can refer to one or more items. It does agree in gender but not in number: even if it refers to a plural noun, the pronoun is in the singular form, not the plural form."