1. While fine articles (PM2.5) pose greatest risks to our health, they are also the main cause of reduced _____ which may threaten traffic safety, as drivers could only see a few meters away on a smoggy day.

2. While invertebrate animals are somehow simple organisms, vertebrate animals, with a on the central line of the body, are more advanced creatures including fish, amphibians, reptiles, birds and mammals, most of which have _____ body parts with their vertebrate as the axis.

3. While things that could be quickly turned into cash, including cash itself of course, are called liquidity, _____ _____ include items that are not easy, if not impossible, to be sold and become money. Examples include cars, houses, machines and land.

4. While Tylenol is an effective medicine for curing a cold, it has strong _____ _____ such as dizziness, dry eyes, muscle fatigue and strong drowsiness.

5. While you go crazy when preparing for an exam, think about the lines in the _____ to the _____ _____ (written by the English poet Percy Bysshe Shelley): if winter comes, can spring be far behind? Believe in yourself and you will see the light at the end of the tunnel!