Which of the following is a prime number? 
Overseas Competition->Knowledge Point->Number Theory Modules->Prime and Composite Numbers->Determining Prime and Composite Numbers
We note that the other options are not prime numbers because:  $38 = 2 \times 19$  $45 = 4 \times 9$  $57 = 3 \times 19$  Hence by the process of elimination, $53$ is a prime number. 