Ex. 5 Complete the following sentences with words or expressions from the passage. Change the form where necessary. 1. Our English class is conducted ________ twice-a-week ________. 2. The farmers have ________ the bare hills ________ rich farmlands. 3. Scientists have long ________ that lung cancer is associated with smoking. 4. Although vitamins ________ health, you cannot skip the traditional health measures like exercising and having a low-fat diet. 5. I work best ________, while he can get nothing finished without help from others.