Answer:
D. Flooding occurs when too much rain falls upstream.
Explanation:
Flooding is not a change in a watershed.
A, B, and C are wrong. They all represent changes in a watershed.
<u>1) find molar mass of CH₄</u>

<u>2) determine moles of CH₄</u>

<u>3) multiply by avogadro's number</u>

Scientists use a Graduated Cylinder
Answer:
Most viscous to least viscous: 
Explanation:
For hydrocarbons, viscosity increases with increasing molar mass. Because increasing molar mass signifies increase in number of electrons in molecules.
We know that in non-polar hydrocarbons, only van der waal intermolecular force exists. Van der waal force is proportional to number of electrons in a molecule.
Therefore with increasing molar mass, van der waal force increases. hence molecules gets more tightly bind with each other resulting increase in viscosity.
Here molar mass order : 
Therefore viscosity order : 