In the united states, the average age of menarche has since the mid-nineteenth century. a. increased marginally
b. declined significantly
c. increased significantly
d. not changed

b. Declined significantly

Explanation:

There were some studies of the timming of menarche, From the sixth to the fifteenth centuries in Europe, most women reached menarche on average at about 14, between the ages of 12 and 15, but earlier years studies found that fewer than 10% of U.S. girls start to menstruate before 11 years of age, and 90% of all US girls are menstruating by 13.8 years of age, with a median age of 12.4 years.

Image attached extracted from : Boaz, N.T. (1999): . Essentials of biological anthropology. Prentice Hall, New Jersey,

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.

b because thats the naswer i got