It is a prehistoric bug that is mostly closely related to the arachnids of today. I lacks a spinneret though. It is one of the first trigonotarbids to ever be described. (It looks like a spiky tick. Seriously)
Answer: The answer is D: to allow maximum exposure to light and to reduce shading of lower leaves.
Explanation:
The arrangement of leaves on a Stem is known as Phyllotaxy. It is used to enable them obtain maximum exposure to sunlight.
Leaves are classified as either alternate, spiral or opposite.
Leaves with alternate pattern arise at a different point (node) on the stem. This helps reduce shading of the lower leaves.