A、They help farmers keep diseases in check. B、Many species remain unknown to scientists. C、Only a few species cause trouble to h

Scientists have identified thousands of known ant species around the world— and only a few of them bug humans. Most ants live in the woods or out in nature. There, they keep other creatures in check, distribute seeds, and clean dead and decaying materials from the ground. A very small percentage of ants do harm to humans. But those are incredibly challenging to control. They are small enough to easily slip inside your house, live in colonies that number in the tens of thousands to the hundreds of thousands, and reproduce quickly. That makes them good at getting in, and hard to kick out. Once they settle in, these insects start affecting your home. In addition to biting ants, other species can cause different kinds of damage. Some, like carpenter ants, can undermine a home’s structure, while others interfere with electrical units. Unfortunately, our homes are very attractive to ants, because they provide everything the colony needs to survive, such as food, water, and shelter. So how can we prevent ants from getting into our homes? Most important of all, avoid giving ants any access to food, particularly sugary food, because ants have a sweet tooth. We also need to clean up spills as soon as they occur and store food in airtight containers. Even garbage attracts ants, so empty your trash as often as possible, and store your outside garbage in a lidded can, well away from doors and windows.
Questions 16 to 18 are based on the passage you have just heard.
16. What does the passage say about ants?
17. What do we learn from the passage about carpenter ants?
18. What can we do to prevent ants from getting into our homes?