Ans: C
$\begin{array}{lcccccccccc}
9a^2b & = & & & 3^2 & \times & & & a^2 & \times & b \\
12a^4b^3 & = & 2^2 & \times & 3 & \times & & & a^4 & \times &b^3 \\
15a^6 & = & & & 3 & \times & 5 & \times & a^6 & & \\ \hline
\text{L.C.M.} & = & 2^2 & \times & 3^2 & \times & 5 & \times & a^6 & \times & b^3 \\
\end{array}$
$\begin{array}{lcc}
\text{L.C.M.} & = & 180a^6b^3 \\
\end{array}$
$\begin{array}{lcccccccccc}
9a^2b & = & & & 3^2 & \times & & & a^2 & \times & b \\
12a^4b^3 & = & 2^2 & \times & 3 & \times & & & a^4 & \times &b^3 \\
15a^6 & = & & & 3 & \times & 5 & \times & a^6 & & \\ \hline
\text{L.C.M.} & = & 2^2 & \times & 3^2 & \times & 5 & \times & a^6 & \times & b^3 \\
\end{array}$
$\begin{array}{lcc}
\text{L.C.M.} & = & 180a^6b^3 \\
\end{array}$
