A、They are expensive to make. B、They are extremely accurate. C、They were first made in space. D、They were invented in the 1970s.

Some people wonder why countries spend millions of dollars on space projects. They want to know how space research helps people on Earth. Actually, space technology helps people on Earth every day. This is called "spin-off technology". Spin-off technology is space technology that is now used on Earth. In early space programs, such as the Apollo missions of the 1960s and 1970s, and in the space shuttle missions today, scientists developed objects for the astronauts to use on the moon and in space. We now use some of these objects every day. For example, we have quartz crystal clocks and watches accurate to within one minute a year. We purify the water we drink with the water filter designed for the astronauts’ use in space. The cordless, hand-held tools we use in our homes, such as vacuum cleaners, flashlights, drills and saws came from the technology of these early space programs. On cold winter days, we can stay warm with battery-operated gloves and socks, and specially-made coats and jackets. All these clothes are similar to the spacesuit designs that kept astronauts comfortable in the temperatures of the moon, and are spin-offs from space technology. These products are only a few examples of the many ways space technology helps us in our everyday lives. No one knows how new spin-off technology from the International Space Station will help us in the future.
16. What do some people want to know about space exploration?
17. What did scientists do for the space shuttle missions?
18. What does the speaker say about quartz crystal clocks and watches?