The correct option is A She says she is ready to take up the job
A complex sentence is made up of two or more clauses, where at least one
of them should be independent, i.e., complete in meaning. The other
clause(s) should be dependent; it should depend on the
main/independent clause for its complete meaning. In the given sentence, the first clause "She says she is ready....the job" is independent; on its own, it is complete in meaning. Hence option A is correct. Option B is an infinitive phrase, it's not a clause. Option C is a subordinate clause; it begins with the subordinating conjunction pair "provided that" and cannot stand on its own as a sentence. Hence options B and C are incorrect. Option D is incorrect because the answer lies in A.