smc

Given three positive integers $a,b,$ and $c$. Their greatest common divisor is $D$; their least common multiple is $M$. Then, which two of the following statements are true? $$\begin{gathered} \text{(1)}\text{the product MD cannot be less than abc} \\ \text{(2)}\text{the product MD cannot be greater than abc} \\ \text{(3)}\text{MD equals abc if and only if a,b,c are each prime} \\ \text{(4)}\text{MD equals abc if and only if a,b,c are each relatively prime in pairs}\text{ (This means: no two have a common factor greater than 1.)} \end{gathered}$$