As a Seed Germinates,its Shoot Points Upward Toward Light,and Its

As a seed germinates,its shoot points upward toward light,and its root grows downward into the soil.Turn the plant sideways,and the stem and roots bend according to the new direction of gravity.How do roots and shoots respond to gravity?

A) by the absorption of light by phytochromes
B) through circadian rhythms
C) through thigmotropism
D) by sensing the photoperiod
E) by the movement of plastids in root cap cells