The least common multiple of 9, 18, and 12 is _____.

The correct option is C 36
$\begin{array}{cc}3& 9,18,12\\ 3& 3,6,4\\ 2& 1,2,4\\ & 1,1,2\end{array}\text{LCM}=3\times 3\times 2\times 2=36$

OR

Multiples of 9 are 9, 18, 27, 36, 45, 54, 63, 72 ... and so on.

Multiples of 18 are 18, 36, 54, 72, 90, ... and so on.

Multiples of 12 are 12, 24, 36, 48, 60, 72, 96, ... and so on.

Common multiples of 9, 18 and 12 are 36, 72,... and so on.

$\therefore$ The LCM of 9, 18 and 12 is 36.