Question14. For any integer $a$, show the following: (a) $\operatorname{gcd}(2 a+1,9 a+4)=1$. (b) $\operatorname{gcd}(5 a+2,7 a+3)=1$. (c) If $a$ is odd, then $\operatorname{gcd}(3 a, 3 a+2)=1$.