girls who experience harsher punishment by their mothers during their preschool and young childhood years are likely to

Girls who experience harsher punishment by their mothers during their preschool and young childhood years are likely to experience an earlier onset of menarche.
Menarche refers to the first menstrual cycle, the first time a girl gets her period. It is a known fact that menstruation is often linked with emotions, especially negative ones, so if girls are being constantly punished about something they may or may not have done, it will affect their bodies as well as their minds.

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

explanation:

productive can also mean:

producing or giving rise torelating to or engaged in the production of goods, crops, or other commodities.

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

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