Problem #PRU-100572

Problem

a) The number $a$ is even. Should $3a$ definitely also be even?

b) The number $5c$ is divisible by $3$. Is it true that $c$ is definitely divisible by $3$?

c) The product $a\times b$ is divisible by $7$. Is it true that one of these numbers is divisible by $7$?

d) The product $c\times d$ is divisible by $26$. Is it true that one of these numbers is divisible by $26$?