Question

ddt is a synthetic substance that was developed for use as a pesticide for crops. it was a very effective pesticide, and it was widely used for many years. however, scientists then discovered that it was harmful to ecosystems and to human health. use of ddt for most purposes is now banned in most countries.
which statement about synthetic materials is best supported by the example of ddt?
a. naturally occurring materials usually accomplish their purpose more effectively than synthetic materials.
b. negative effects of synthetic materials may not be known until the materials are already in use.
c. the harmful effects of synthetic materials usually outweigh their benefits.
d. most synthetic materials are harmful to people and animals, but most natural materials are not.

Explanation:

DDT was used widely first (effective pesticide) then its harmful effects (to ecosystems/human health) were discovered later, leading to a ban. This matches the idea that negative effects of synthetic materials may not be known until after use. Other options are unsupported: A compares effectiveness (not stated), C claims harms usually outweigh benefits (not generalizable), D says most synthetic materials are harmful (too broad).

Answer:

B. Negative effects of synthetic materials may not be known until the materials are already in use.