Answer: A Conjunctions are words that link other words, phrases, or clauses together. Subordinating conjunctions join independent and dependent clauses. Subordinating conjunction can signal a cause-and-effect relationship, a contrast, or some other kind of relationship between the clauses. Common subordinating conjunctions are because, since, as, although, though, while, and whereas.These show relation in time, place or condition.Until is used to depict 'up to the time or point that something happenedtill is sometimes used instead of until. In the given sentence it is inferred that the person is to wait up to the time I come back. ThusOption A is correct.Aftershows subsequently to the time when: It is inappropriate n the given sentence as it is logically incorrect. Thus Option D is ruled out. Beforeshows earlier than the time that. It is logically and grammatically incorrect to use it in the sentence. Thus Option C is discarded. Option B is also incorrect as 'besides'
is used to introduce additional information. and it doesn't have any relevance to the sentence given.
The time taken for 90% of a first order reaction to complete is approximately: (A) 1.1 times that of half-life (B) 2.2 times that of half-life (C) 3.3 times that of half-life (D) 4.4 times that of half-life