I just need question 19 answers please help.

A is the answer

Explanation:

in depth explaination  

Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities. This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water – hence the name photosynthesis,  "light", and sunthesis , "putting together". In most cases, oxygen is also released as a waste product. Most plants, most algae, and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies most of the energy necessary for life on Earth.

C. Lactic acid fermentation

Explanation:

What is the process of lactic acid fermentation?Lactic acid fermentation has two steps: glycolysis and NADH regeneration. During glycolysis, one glucose molecule is converted to two pyruvate molecules, producing two net ATP and two NADH.