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

The correct answer is (A) climbing up into the canopy.

Vines are the plants that grow like climbers. They grow from bases on long stem and they move in a climbing pattern. All the vines are not sun facing some of them grow against sunlight but some other plants like grapevine grow by climbing up into the canopy. They do so to compete for sunlight.

b. the carbon cycle ensures living things have a source of hydrogen

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.