·sea voyage of a month or more · between africa and the americas · approximately 12 million people made the journey · a death rate of approximately 25% during the journey these are all describing

The sentences are describing the Transatlantic slave trade.

Explanation:

The transatlantic slave trade was the transport of slaves from West Africa across the Atlantic to America that continued during the early modern period, from the 16th century to the 1850s, when slave trade and slavery were prohibited.

The trade was part of the so-called triangle trade, where ships arrived in West Africa with European goods, which were used to buy slaves from domestic slave traders; brought slaves to America's plantations, from which they extracted export crops such as cotton and tobacco, which were then brought back to Europe.  

the answer to your question is,

d. when a child was born.

-mabel < 3

answer; no longer than a reasonable period of time;