Why is there a leap year every four years?

Which ocean zone has the most abundant primary producer and why a) the abyssopelagic zone ,du to the absence of light and cold water temperatureb) the bathypelagic zone, due to the absence of light and cold water temperaturec) the mesopelagic zone ,due to uts high light availability and warm water temperature d) the epipelagic zone, due to its high light availability and warm water temperature

How many grams of aluminum will there be in 98g of al2o3?

Glucose (c6h12o6) is an important biological molecule. (round the answer to nearest hundredth.) what is the percent by mass of carbon in glucose?