Fill in the blanks with the words given below. Change the form where necessary. Each word can be used only once.16. In playgrounds, children create a _____ based on physical abilities, with the tough ones taking the lead.17. It is generally _____and coherent, with some fluidity of expression, though it exhibits some noticeable lapses in the expression of ideas.18. Please put this _____ under your armpit and let me feel your pulse.19. Sometimes, of course, our markings may be simply a matter of _____.20. Caffeine is the active _____ of drinks such as tea and coffee.