A. 213444

B. 214344

C. 214434

D. 231444

**Answer:**A. 213444

**Explanation:**
L.C.M. of 21, 36, 66 = 2772.

Now, 2772 = 2 x 2 x 3 x 3 x 7 x 11

To make it a perfect square, it must be multiplied by 7 x 11.

So, required number = 2^{2} x 3^{2} x 72 x 11^{2} = 213444