Why is the whole arm used instead of only the fingers while making a long straight line?

Correct answer: To keep the movement steadier and more continuous

The governing concept is coordinated arm movement in drawing and painting. A long line requires the brush to travel in one direction over a considerable distance. Moving from the shoulder and arm gives a wider, steadier range of motion and reduces the small irregular movements caused by using only the fingers. Thus option D is correct. The other choices concern neither line stability nor the mechanics of making a long stroke.