Problem:OPTIONS:
- temperature changes
- to leave the egg
- fertilization
- competition
- it needs them
- to feed
- permineralization
- to heal themselves

You are presented with the quiz "Why do male gametes swim from male to female reproductive organs?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "sperm had to swim from male to female reproductive organs for fertilization" and "male gametes are called sperm". So, what's the best answer to the question?
****
A: fertilization

Problem:OPTIONS:
- alleles
- Toxicity
- Pollution
- food
- diseases
- cells
- pores
- microbes

You are presented with the quiz "Viruses cause contamination spreading what?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "viruses cause many human diseases" and "bacterial contamination can spread diseases to humans and livestock". So, what's the best answer to the question?
****
A: diseases

Problem:OPTIONS:
- deforestation
- deserts
- cigarettes
- desertification
- humans disturb it
- environments
- weather
- harmful substances

You are presented with the quiz "what has a negative impact on the environment?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "erosion of soil has a negative impact on the environment" and "desertification implies soil erosion". So, what's the best answer to the question?
****
A: desertification

Problem:OPTIONS:
- hurricanes
- wind tunnels
- dangerous
- forces
- kalenchoes
- flooding
- high populations
- Sediment

You are presented with the quiz "what are most canyons formed by over long periods of time?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "most canyons are formed by flowing rivers through erosion over long periods of time" and "most river erosion occurs when the river is in flood". So, what's the best answer to the question?
****
A:
flooding