How can you use a single parallel sentence to combine the sense in these two sentences? i regularly drudge five days a week. i habitually sleep through the weekends. i am used to drudging five days a week and sleep through the weekends. i am used to drudging five days a week and sleeping through the weekends. i am used to drudge five days a week and to sleep through the weekends. i am used to drudge five days a week and sleeping through the weekends.

The correct answer is 'I am used to drudging five days a week and sleeping through the weekends", because in a parallel sentence, there has to be the same form of the verb, in this case it is a participle. The other examples cannot be correct, because the scheme differs (the first verb is a participle, and the second one is infinitive, or vice versa, which is not correct in a parallel sentence) and "I am used to drudge five days a week and to sleep through the weekends" could be correct because there is the same verb form (both are infinitives), but since 'used to' has to be followed by a verb + -ing, it cannot be correct.