What is the name of the valve that keeps blood from flowing backward into the left ventricle?

What did the first language sound like

Ricardo notices that when he plays soccer in the rain, his ball does not seem to go as far after a kick. what is the best scientific question that ricardo could ask about this observation? is soccer better played in the rain or sun? how does rain affect the distance a soccer ball can travel? how does rain affect the speed of a soccer ball? is soccer affected by the rain?

Explain how the political influence of african americans leaders became weaker.