The chart shows births per thousand residents from 1935 to 1970. A line graph titled Birthrate, 1935 to 1970 shows years on the x axis and births per 1,000 population on the y axis. The line starts at 18 in 1935, to 20 in 1945, to 24 in 1950, to 25 in 1955, to 23.5 in 1960, 19 in 1965, to 17 in 1970.

What was a cause of the significant increase in birthrate shown on the graph?
A. couples had babies during World War II.
B. Economic prosperity in the 1960s led couples to have larger families.
C. After World War II, couples wanted to settle down and raise children.
D. The US government gave financial incentives for couples to have children.