I would say that B. is the right answer.
All numbers that only have one and itself as factors are prime. Therefore, to tell if a number is prime simply find it's factors. If it has more than two factors than it is not a prime number.
Answer:
(C)4
Step-by-step explanation:
Given the line: 
The gradient of the line, 
A line perpendicular to the given line will have a gradient,
(by definition of perpendicularity).
Therefore, a perpendicular line that passes through the point (4,1) is:

Comparing with the slope-intercept form y=mx+x, the slope of the perpendicular line, b=4.
It add by the number in the first column.
1 + 1 = 1
2+1=3
3+2=5
5+4=9