ITMC 2018 Grade 5 National Preliminary set01 Question 7

A factor of n is a positive integer that divides n. For example, the six factors of 12 are 1, 2, 3, 4, 6 and 12; the two factors of 3 are 1 and 3; and 1 has only one factor. Which of the following numbers has the fewest factors?