The most successful settlement in north america was in the subtropical district at the mouth of the mississippi river in what is now louisiana, where some 300 settlers and 4000 african slaves founded sugar plantations.

French.

Explanation:

Louisiana has a multicultural heritage. As the exercise mentions, the biggest colony was french but there were also Haitian, native american, african and spanish cultures clashing in that territory. Before buying the territory in 1803, Louisiana had been mostly a French colony (for a short period a Spanish one) having imported many slaves from Africa, as the exercise details.

answer; (true);

answer; eliminate parking problems in cities, because a car took up only half as much space as a horse and buggy;