Answer:
B.
Step-by-step explanation:
The others are incorrect. A. contains "when I am in town last year", making its verb tense convoluted and inaccurate. C. contains "called them when I go there again", making the verbs tenses switch mid-sentence and very incorrectly. D. contains "do not contact my cousins when I was in town", making its tenses unclear and also incorrect as well.
When in doubt. think about how the sentence flows. If it sounds off or odd, it is probably incorrect. Envision saying the sentences yourself. Does it feel proper? Always think about how it sounds when actually being spoken, as that can help eliminate mistakes.