Gap 1: because / because of / although / despite. The gap is followed by a noun phrase (a reduction in staff), not a clause. The idea is a reason. → because of
Gap 2: apply / will apply / applied / applying. The sentence describes the future (from 1 March, for at least six months). → will apply
Gap 3 (sentence choice): (A) The library was built in 1965. (B) Weekend opening hours will not change. (C) Please return the books you borrowed. (D) The new café is very popular. The text is about changes to opening hours, and the next sentence gives practical help for weekday users. Only (B) continues the topic of hours. → (B)
Gap 4: extreme / extremely / extremes / extremity. The gap describes the adjective grateful, so it must be an adverb. → extremely
Complete the Words example: “Most adults need se___ to nine hours of sleep.” A number before to nine, and three letters are missing → seven (type ven).