What are the pulrals?

Where is 1 fifth on a ruler? Why must an experiment be repeated many times? Why can air be squashed but not water? 40mm is how many cm? Why is a sea breeze thunderstorm considered a type of air mass thunderstorm? What were the results of Mendel's first experiment? Where must you cite your sources in a research paper? What unit would you use to measure the weight of a baseball? When did reverend Issac Douglas died? What is the acceleration of a 50 kg object pushed with a force of 500 newtons? Which material is ideal for an office door that allows light to pass through but maintains privacy? What was the first thing invented that we now? What is the pH scale based on? What can you conserve? How do constant and variables affect an experiment? What is a force that can cause an object to change its speed and direction? What does it mean if your wbc 4.6 and your rdwsd 14.6? What does it mean Enpsychlopedia? What is the slowest traveling wave? How do you use the word resistance in a sentence?