OG详解-OG9 文法 Q1

Choice A is the best answer. The convention being tested is the use of finite verbs in a relative clause. Relative clauses, such as the one beginning with “which,” require a finite verb, a verb that can function as the main verb of a clause. This choice correctly supplies the clause with the finite past tense verb “provided.” 
Choice B is incorrect because the non-finite participle “having provided” doesn’t supply the clause with a finite verb. Choice C is incorrect because the non-finite to-infinitive “to provide” doesn’t supply the clause with a finite verb. Choice D is incorrect because the non-finite participle “providing” doesn’t supply the clause with a finite verb.