Find the value for lcm $$\left[ 12,18\right]$$. 
Overseas Competition->Knowledge Point->Number Theory Modules->Factors and Multiples->Common Factors and Common Multiples
List the prime factorization for $$12$$ and $$18$$ first. $$12=2^{2}\times3$$ and $$18=3^{2}\times2$$. The largest exponent for $$2$$ is $$2$$, and the larger exponent for $$3$$ is $$2$$, thus the least common multiple for $$12$$ and $$18$$ is $$2^{2}\times3^{2}=36$$. We choose $$\text{A}$$. 