Can someone help me asap

When lactate builds up in a runners muscles it causes a burning sensation what causes this to occur

Which best describes carbon dioxide’s path out of the body

What are the two causes of density in deep current waters? a. salinity (how much salt) of the water and high temperaturesb. salinity (how much salt) of the water and low temperatures c. oxygen content of the water and high temperatures. d. oxygen content of the water and low temperatures