Fact 1: Some viruses live in a dormant state inside the body.  Fact 2: When ferns are dormant it is as if they are hibernating.  Given the two facts above, answer the question "What can stay hidden in a hibernating state inside the body?" with the following options:  - infections  - blood cells  - fungi  - insects  - viruses  - honeybees  - plasma  - barnacles
viruses
Fact 1: Most mollusks have shells.  Fact 2: Coral reefs and shells are made of calcium carbonate.  Given the two facts above, answer the question "What do mollusks contain?" with the following options:  - harmful substances  - Organic compounds  - bacon  - cayenne  - acetic acid  - dogs  - Chlorophyll  - Calcium carbonate
Calcium carbonate
Q: Fact 1: Erosion causes a river to become deeper and wider.  Fact 2: Weathering and erosion continue to shape it today.  Given the two facts above, answer the question "Weathering causes what to become deeper and wider?" with the following options:  - a landslide  - Sediment  - a mountain  - a volcano  - soils  - rock  - flooding  - a river
A: a river
Question: Fact 1: Electricity sometimes is used for heating buildings.  Fact 2: Hospitals incorporate most types of technical systems encountered in other types of buildings.  Given the two facts above, answer the question "what is electricity sometimes used to heat?" with the following options:  - space  - hospitals  - waves  - direct energy  - energy  - Light  - condensation  - clouds
Answer: hospitals
*Question*
Fact 1: Cold fronts cause thunderstorms as they pass by.  Fact 2: If cold air is advancing on warm air, the front is called a cold front.  Given the two facts above, answer the question "Which situation can cause a thunderstorm?" with the following options:  - Fog rising over a lake  - pressure differences.  - Earth's axis of rotation is tilted  - Setting up lightning rods  - Cold air advancing on cold air  - Cold air advancing on warm air  - Changing the angle of the sun  - fall moving to winter
**Answer**
Cold air advancing on warm air
(Q).
Fact 1: Air pollution harms the respiratory and circulatory systems.  Fact 2: Air pollution is caused by lots of different pollutants.  Given the two facts above, answer the question "What systems are pollutants bad for?" with the following options:  - destroying life  - classification system  - an organism's body  - respiratory and circulatory  - animal habitats  - ambulatory systems  - social security system  - the environment
(A).

respiratory and circulatory