A good way to figure out the relationship in a given question is to make up a sentence that describes the relationship between the first two words. Then, try to use the same sentence to find out which of the answer choices completes the same relationship with the third word.
An optimist is a person whose outlook is cheerful. A pessimist is a person whose outlook is gloomy. The answer is not (choice b) because a pessimist does not have to be mean. (Choices c) and d are incorrect because neither adjective describes the outlook of a pessimist.
A lizard is a type of reptile; a daisy is a type of flower. Choices a and b are incorrect because a petal and a stem are parts of a flower, not types of flowers. (Choice d) is incorrect because an alligator is another type of reptile, not a type of flower.
A sponge is a porous material. Rubber is an elastic material. (Choice a) is incorrect because rubber would not generally be referred to as massive. The answer is not (choice b) because even though rubber is a solid, its most noticeable characteristic is its elasticity. Choice d is incorrect because rubber has flexibility.