All the energy available to humans has its origins in

The sun

Explanation:

This is because humans are heterotrophs, meaning they source their energy from the other organism by feeding on them. The food chains begin with primary producers that convert the energy from the sun into biomass through the process of photosynthesis. This energy rises up the food chain as the primary producers are fed on by consumers (humans included).

answer; the tunica intima also called tunica interna, consists of elastic fibers,connective tissue and smooth muscle cells;

evidence and logical support is essential for a scientist to do in order to maintain credibility. this is because no one can believe without any logic and without any evidence.hence a scientist can maintain credibility by proving himself and by answering logically so experiments prove very beneficial. logical hypothesis give conclusion which is acceptable. therefore, there are two main factors to maintain credibility by a scientist is evidence and logical support.