*Question*
Q: Deep ocean currents are caused by differences in what property at the top and bottom?    Choices:  - diameter  - mass  - velocity  - density  A:
**Answer**
density

*Question*
Q: What are the two types of endoplasmic reticulum?    Choices:  - thick & smooth  - rough & thin  - rough & thick  - rough & smooth  A:
**Answer**
rough & smooth

*Question*
Q: What are the two most abundant elements in the universe?    Choices:  - hydrogen and oxygen  - nitrogen and carbon  - oxygen and carbon  - hydrogen and helium  A:
**Answer**
hydrogen and helium

*Question*
Q: Which system carries out long-distance transport of materials between the root and shoot systems?    Choices:  - circulatory tissue system  - reproductive tissue system  - perceptual tissue system  - vascular tissue system  A:
**Answer**

vascular tissue system