This is the first mobile phone ()I boughtThis is the first mobile phone _____ I bought.A.which.B.that.C.when.D.who

This is the first mobile phone ()I boughtThis is the first mobile phone _____ I bought.A.which.B.that.C.when.D.who
This is the first mobile phone ()I bought
This is the first mobile phone _____ I bought.A.which.B.that.C.when.D.who

This is the first mobile phone ()I boughtThis is the first mobile phone _____ I bought.A.which.B.that.C.when.D.who
B,用that,因为mobile phone 有the first修饰,