Vines most successfully compete for sunlight in tropical rainforests by

a) climbing up into the canopy

b) strangling the trees they grow on

c) having broader leaves that absorb more light

d) having thick, woody stems

Vines are plants that are trailing woody and they belong to the grape family. Being in the forest, sun is blocked by the high tress that surround the area. The vines are then left with no sunlight. So they crawl and grown up the canopy to get their share of sunlight. 
The answer is a. climbing up the canopy.