$$\text{A}$$: $$76186\div2=28093$$. But $$28093$$ is not divisible by $$2$$. So, $$76186$$ is divisible by $$2$$ but not $$4$$, $$76186$$ is not a perfect square.  $$\text{B}$$: $$750235\div5=150047$$. But $$150047$$ is not divisible by $$5$$. So, $$750235$$ is divisible by $$5$$ but not $$25$$, $$750235$$ is not a perfect square.  $$\text{C}$$: $$921438\div2=460719$$. But $$460719$$ is not divisible by $$2$$. So, $$921438$$ is divisible by $$2$$ but not $$4$$, $$921438$$ is not a perfect square.  Thus, answer must be $$\text{D}$$. In fact, $$2660161=7^{2}\times233^{2}$$. 
Only one of the following four numbers is a perfect square. Which one is it? 
Options:
  $$76186$$ 
  $$750235$$ 
  $$921438$$ 
  $$2660161$$ 