(a) The sentence should be corrected to: "There has been a debate over what an antique is for years." The word "have" should be changed to "has" to agree with the singular subject "debate".
(b) The sentence should be corrected to: "Some say an antique is an object of considerable age valued for its aesthetic or historical significance." The word "a" should be added before "considerable" to make the sentence grammatically correct.
The corrected question numbers and words are: (a) "1. have" to "has"; (b) "considerible" to "considerable" and add "a" before "considerable".