During a Viticulturist's Presentation on Growing and Managing Grapes, Why

During a viticulturist's presentation on growing and managing grapes, why did he state that it is imperative to encourage the grapevine's natural tendency for positive thigmotropism?

A) To encourage the vine's response to move toward the early morning light as opposed to the late afternoon sun.
B) To encourage the roots to grow deeper and spread out.
C) To encourage the grapes to retain their sugar for a longer period of time.
D) To encourage the twining stems to wrap around the supporting wires.