If the Labour Market Is Perfectly Competitive, Labour Demand Function

If the labour market is perfectly competitive, labour demand function is given by ND = a + bW and labour supply function is given by NS = c + dW; W is the wage rate. At market equilibrium, we can determine the market wage rate as:

A) (a + c) /(d + b) .
B) (a - c) /(d - b) .
C) (a + c) /(d - b) .
D) (a - c) /(d + b) .
E) (d + b) /(a + c) .