A、The low birthrate in the last 20 years. B、The increase of multiple births. C、The trend of economic condition. D、The assisted r

The rate of twin births in the United States reached a record high in 2014, according to an annual report released Wednesday by the Centers for Disease Control and Prevention’s National Center for Health Statistics. There were 33.9 twins born for every 1 000 births in 2014. The twin birthrate has been climbing most years since 1980 among white, black and Hispanic women. Between 2013 and 2014, however, it only went up among black women, by 4%, whereas the rates did not change among white and Hispanic women. Births of triplets and higher multiples were on the rise from 1980 to 1998, when the rate peaked at 193.5 multiples for every 1 000 births. But unlike twin births, the rate has been declining for 20 years. Between 2013 and 2014, it dropped 5% to 113.5 per 1 000 births. The overall increase in twin and multiple births could be due in part to the assisted reproductive technology. Use of the technology has been on the rise since the first baby was conceived using this technology in the United States in 1981.
5. What is the main idea of the news item?
6. In 2013 and 2014, which group of people had an increased rate of twin babies?
7. What is the cause of the change according to the news?