Problem: OPTIONS:
- nitrogen
- warmth
- air
- water
Q: Q: What is needed by all known forms of life?   A:
Answer: water
Problem:OPTIONS:
- clear
- opqaue
- secreted
- pigmented

Q: Photoreceptors in each ocellus receive light only through the opening where there are none of which cells?   A:
****
A: pigmented
Q: Coral reefs and tropical rainforests are ecosystems known for what, contributing greatly to the species in existence on earth?   A:
OPTIONS:
- commensalism
- mass migrations
- spontaneous mutation
- biodiversity
biodiversity
Q: What part of the cell helps it keep its shape?   A:
OPTIONS:
- nucleus
- cytoplasm
- enzymes
- cytoskeleton

Answer: cytoskeleton
Question: Q: The heart, blood vessels, and blood make up which system in the body?   A:
OPTIONS:
- digestive
- pulminary
- respiratory
- cardiovascular
Answer: cardiovascular
input: OPTIONS:
- by age
- by distance
- by size
- by color Now, answer this question: Q: What is the most common way to classify stars?   A:
A:
output:
by color