A lactic acid test is a blood test that measures the level of lactic acid made in the body. Most of it is made by muscle tissue and red blood cells.
A biofuel is a fuel that is produced through contemporary biological processes, such as agriculture and anaerobic digestion, rather than a fuel produced by geological processes such as those involved in the formation of fossil fuels, such as coal and petroleum, from prehistoric biological matter.
Biofuel is renewable because the process that generates the fuel is ongoing. Trees can be regrown, sewage can be converted into methane, and oil and alcohol can be generated from various plants. Biofuel takes carbon dioxide from the air as the original vegetation grows, and returns it when burnt, so it has a neutral carbon footprint.