Ancient sailors and farmers did not have satellites and computers to help them forecast the weather. They observe the sky, winds and clouds. Eventually, patterns emerged and people made up sayings to remember them.We now realize that behind the sayings often lies real science. Here are two time-tested sayings, and the climate reasoning backing them up."When the dew (露水) is on the grass ," rain will never come to pass. " Clear skies at night lower temperatures enough for humidity (湿度) to condense as dew. So a heavy dew forms on a summer night, except a fair day. But "when grass is dry before the morning light, 10ok for rain before night. " This is especially true if temperatures rise during the night as a result of increasing cloud cover. "If night has a fever, it cries in the morning. "If with your nose you smell the day, some weather is on the way. Plants release oil into the atmosphere, and research indicates that the higher the humidity is, the more oils the plants gives off. This produces the distinctive smell many of us recognize when we say: "Smells like rain today. \ According to the passage, how do today’s people forecast weatherToday’s people forecast weather with the help of（）.