3. Why do the plates that make up the Earth's crust move? A. because the Earth's outer crust is thin

B. because the Earth's inner core is solid

C. because pressure within the planet forces them to shift

4. What is the immediate effect of weathering?

A.
Sediment forms into sand dunes.

B. Rock is broken down into smaller pieces.

C. Sediment is moved from one place to another

5. Why are many settlements built in river valleys?

A. because the soil is fertile

B. because of travel desires

C. because of mineral deposits

3- C

4- B

5- A

Explanation:

C because our core is super hot and condensed, and the crust floats on the mantle. Convection currents move throughout the mantle pushing the crust.

B because weathering is a natural way of wearing away and breaking down rocks and soil. The others are just moving it.

And finally, letter A because river valleys mean fertile soil. Fertile soil is great for farming and raising crops and animals. Most of the greatest civilizations were in valleys such as:

the Chinese in by the Yellow River

the British by the Thames River

the Indians by the Ganges River

lots of civilizations by the Seine

plenty on the Nile

and so many along the Euphrates and Tigris.

They all had fertile soil around their banks making a crade for civilization.

simplify brackets

8 - 2a - 7 = a + 40

simplify 8 - 2a - 7 to -2a + 1

-2a + 1 = a + 40

add 2a to both sides

1 = a + 40 + 2a

simplify a + 40 + 2a to 3a + 40

1 = 3a + 40

subtract 40 from both sides

1 - 40 = 3a

simplify 1 - 40 o -39

-39 = 3a

divide both sides by 3

-39/3 = a

simplify 39/3 to 13

-13 = a

switch sides

a = -13