input with options: Q: Deep ocean currents are caused by differences in what property at the top and bottom?   A:
output: density

input with options: Q: What are the two types of endoplasmic reticulum?   A:
output: rough & smooth

input with options: Q: What are the two most abundant elements in the universe?   A:
output: hydrogen and helium

input with options: Q: Which system carries out long-distance transport of materials between the root and shoot systems?   A:
output:
vascular tissue system