The correct answer is E. No error.
The sentence “He is a mason who built my house” is grammatically correct. The subject “He” is singular, and the verb “is” is also singular. The relative clause “who built my house” modifies the noun “mason,” and it is correctly introduced by the relative pronoun “who.” The sentence is also clear and concise, and it conveys the intended meaning accurately.
Option A, “He is,” is correct. The subject “He” is singular, and the verb “is” is also singular.
Option B, “a mason,” is correct. The relative clause “who built my house” modifies the noun “mason,” and it is correctly introduced by the relative pronoun “who.”
Option C, “who,” is correct. The relative clause “who built my house” modifies the noun “mason,” and it is correctly introduced by the relative pronoun “who.”
Option D, “built my house,” is correct. The relative clause “who built my house” modifies the noun “mason,” and it is correctly introduced by the relative pronoun “who.”
Option E, “No error,” is correct. The sentence “He is a mason who built my house” is grammatically correct.