III. Reading Comprehension: Choose the most appropriate answer. (2 points each； 40 points intotal)Passage A: Questions 31-36        Most animals use more than one species as food. Therefore, the term 'food web' is a betterdescription of food relationships than ~food chain." A food web is a complex feeding system thatcontains several food chains. For example, mice, rabbits, and deer eat plants. Owls cat mice andrabbits. Mountain lions eat rabbits and deer. These five species are parts of food chains thantogether form a food web.        The first link in a food chain is always a green plant. Only organisms with chlorophylI, such asgreen plants, can make food. For example, the first link in aquatic food chains is algae. Most algaeare microscopic green plants that produce food by photosynthesis. In photosynthesis, energy fromsunlight converts carbon dioxide and water to sugar. Tiny fish in lakes, streams, and oceans eatalgae. In turn, these tiny fish are eaten by larger fish. The larger fish are eaten by still larger fish. The food supply for fish is made by algae. This food is then passed through the food chains as oneanimal eats another.        Organisms may be divided into three groups based on how they obtain food. These groups areproducer, decomposer, and consumer. Organisms containing chlorophyll are producers. Thus, greenplants are producers. Animals that eat other animals and plants are consumers. Microbes,once-celled organisms that causes the decay of dead plants and animals, are decomposers. Sincedecomposers cannot make their own food, they are also consumers.
【題組】31. The main purpose of the passage is to
(A) determine which food chain is the most efficient.
(B) describe the food network among plants and animals.
(C) explain the process of photosynthesis in green plants.
(D) appeal to conservationists to protect endangered plant species.