Which of the following statements are false: Some veins have valves that aid in the one-way propagation of blood. Some veins depend on the activity of skeletal muscles to conduct blood. The endothelial lining of veins is smooth. Veins always conduct blood towards the heart. Veins only conduct oxygen poor blood.

Veins don’t always conduct oxygen poor blood. The pulmonary vein brings reoxygenated blood from the lungs into the heart

Humans can affect weathering and erosion in several ways.  humans cause  increases in acid rain and pollution, which increase the amount of  weathering  agents in the air and water, and then on land.for an easy answer: 1) acid rain2) pollution

The answer to this will be from your lab notes/procedure. it would be best to ask another student who participated in the lab as we do not know what was done, what enzyme or if the temperature is celsius or fahrenheit. if i were to guess though i'd say the rate stopped due to enzyme denturing at high temperature