A、air swirls B、moisture C、rainfall D、sinking air D

For those of us lucky enough to always have enough food and water, it may be hard to imagine living through a drought. A drought occurs for a variety of reasons, usually including a lack of rainfall and high temperatures. Soil moisture severely dwindles. Why and how do these meteorological events occur?
    As air swirls around the earth, it rises and sinks over different areas of the globe. When air rises it cools and loses moisture. When air sinks, it grows warmer and absorbs moisture, drying out the land. Sinking air helps to form deserts, such as the Sahara Desert in Africa.
    Warm, sinking air can hamper cloud formation, which results in less rain and lower overall humidity. When these conditions occur in an area that normally receives enough rain to allow plants to grow and keep water sources replenished, a drought can ensue. The Dust Bowl that affected the prairie regions of the United States was one infamous drought. An equally severe drought occurred in the United States in the summer of 1988. Rainfall o-ver the mid-west, Northern Plains, and the Rockies was fifty to eighty-five percent below normal.
    Sometimes over-farming and soil erosion contribute to drought, but there are also natural disasters that can occur when soil is carefully preserved. When a drought hits, there’s little that can be done to end it. Water and soil conservation can help, but until the rains come again there’s not much science can do.
Questions:
14. According to the passage, which results in less rain and lower overall humidity?
15. Which of the following can hamper cloud formation and lead to less rain and lower overall humidity?
16. What can contribute to drought?