In the equation y = kx, the slope of the line is represented by the constant

a.) x

b.) k

c.) y

d.) k+x

K is the constant of proportionality also the same as slope.

You can see the commonality in the equations

y = kx

y = mx + b

The difference is that is a direct proportion the line will always go through the origin so the b will be zero.

The answer is B.