Few is a quantifier used with plural countable nouns. Little is used with singular uncountable nouns. Cities are plural countable nouns. "A few" means some. Option B is correct. Once, I have visited America. I know a few cities there.
The sentence "One of the students was absent today" is in the past tense. The past tense form "was" is used because the action (being absent) occurred in the past relative to the time of speaking, which is today.
. . . . . I use your cell phone as I have forgotten mine?