To find the angle of the sector representing labour in a pie chart, follow these steps:

1. Calculate the total cost of production:

$$\text{Total Cost}=\text{Labour}+\text{Power}+\text{Materials}+\text{Miscellaneous}$$

$$\text{Total Cost}=70+15+30+5=120$$

2. Determine the fraction of the total cost that is due to labour:

$$\text{Fraction for Labour}=\frac{\text{Labour}}{\text{Total Cost}}=\frac{70}{120}$$

Simplify the fraction:

$$\frac{70}{120}=\frac{7}{12}$$

3. Convert this fraction into an angle for the pie chart:

The total angle in a pie chart is ${360}^{\circ }$.

$$\text{Angle for Labour}=\frac{7}{12}\times {360}^{\circ }$$

$$\text{Angle for Labour}=7\times {30}^{\circ }={210}^{\circ }$$

Thus, the angle of the sector representing labour in the pie chart is:

A. 210°