The diagram below shows a plant shoot (coleoptile) exposed to unilateral light:

The following passage outlines the physiological process of phototropism in this shoot:

Auxin is actively transported laterally across the tip, accumulating at ......................... In shoot cells, this high concentration of auxin ........................ cell elongation. This asymmetric growth rate causes the shoot to bend .........................

Which option, A to D, is the correct sequence of missing words to complete the passage?