*Question*
Q: Each new horizontal row of the periodic table corresponds to the beginning of a new period because a new principal energy level is being filled with what? Choices: - protons - photons - neutrons - electrons A:
**Answer**
electrons

*Question*
Q: What type of rain dissolves limestone and marble? Choices: - carbon - natural - sulfur - acid A:
**Answer**
acid

*Question*
Q: What is another name for flatworms such as tapeworms and flukes? Choices: - epiphytes - trematodes - polychaetes - platyhelminthes A:
**Answer**
platyhelminthes

*Question*
Q: What is the name of the outer layer of skin? Choices: - endodermis - hypodermis - the dermis - the epidermis A:
**Answer**
the epidermis