Todos los inviernos, mi familia (ir) a esquiar juntos. a. imperfect b. preterite

The complete sentence would be - 

Todos los inviernos, mi familia va a esquiar juntos.

This is imperfect. Imperfect is used to to talk about events that happen continually; in this case, the speaker's family continually goes skiing (they go every winter).

Preterite tense is used to describe events that have happened and are over.
An example of preterite would be Mi familia y yo fuimos a esquiar el invierno pasado. This sentence conveys that the speaker went skiing with his/her family last winter, but doesn't regularly go skiing with his/her family every winter.

This has your answer: