Understand the term "deflectors" in the context of animal deterrents.

Deflectors are devices or structures designed to turn aside or divert animals from a particular area or object.

• A. Elephants: While large barriers can deflect elephants, the term "deflector" is not the most common or specific term used for elephant deterrents (e.g., electric fences, trenches).
• B. Birds: "Bird deflectors" or "bird diverters" are commonly used on power lines, windows, and in agricultural settings to prevent birds from perching, nesting, or colliding. This is a direct and common application.
• C. Rodents: Rodents are typically deterred by traps, poisons, or physical exclusion (e.g., sealing entry points), not usually by "deflectors."
• D. Monkeys: Monkeys are often deterred by fences, netting, or scare tactics, but "deflectors" is not the primary term.

"Birds" are commonly kept away using specific devices known as deflectors.

The correct option is B.
$\boxed{\text{B. birds}}$

8. One of the following fuels may cause deforestation if used by many people. Which one is it?

Deforestation is the clearing of forests for other land uses, often involving the cutting down of trees.

• A. Firewood: Firewood is obtained directly from trees. Extensive use of firewood, especially in areas where it's a primary energy source, leads to the felling of trees and thus causes deforestation.
• B. Gas: Natural gas or LPG is a fossil fuel. Its use does not directly involve cutting down trees.
• C. Kerosene: Kerosene is a petroleum product. Its use does not directly involve cutting down trees.
• D. Electricity: Electricity is a form of energy, not a fuel source in itself. While its generation (e.g., from hydroelectric dams or coal-fired power plants) can have environmental impacts, including indirect effects on forests, the electricity itself is not derived from trees, and its direct use does not cause deforestation.

Firewood is the only option that directly results in the removal of trees.

The correct option is A.
$\boxed{\text{A. Firewood}}$