a. .. The United States laws that protect endangered Species Are considers to be the strongest in the world. b. Are much weaker than the legal protections in most other countries. c. Are rarely enforced. d. Apply to only 10 species of animals and about 20 species of plants.​

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.

the answer to your question is,

old stone age.

-mabel < 3

a would be the answer

answer; archaeologists;