ACTIVITY 18 Editing Read the paragraph and notice the underlined words. If there is an error, write the correction. PARAGRAPH 6.3 Life on Mars exceto It is possible that life already exist on Mars. Some scientists believe that water have existed on Mars for two or three billion years. Scientists have also discovered methane gas on Mars. On our planet Earth, microbes, single-celled life forms, is able to live on the bottom of the ocean by cat methane. Finding any live on Mars, even microbes, would be one of the bigger scientific discoveries of all time. ACTIVITY 19 | Combining sentences Combine the ideas into one sentence. You may change the word forms, but do not change or omit any ideas. There may be more than one answer. 1. Stars are light years away from Earth. Stars contain a lot of heat. The heat s extreme. 2. Coffee farming can be environmentally friendly Coffee farming can be sustainable. Farmers can still profit from it. 3. There was a period of rain in Kenya. The rain was heavy. It exposed a big crack in the earth. The crack measures 50 feet deep. It measures 65 feet wide