Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: Virtually all animals have internal digestion of food. Animals consume other organisms and may use special tissues and organs to digest them. (Other heterotrophs, such as fungi, absorb nutrients directly from the environment. ). Answer: internal

Answer: What sort of digestion do animals engage in?

Question: Passage: For example, in the fall, when the days start to get shorter, the trees sense that there is less sunlight. The plant is stimulated, and it sends messages telling the leaves to change colors and fall. This is an example of photoperiodism , the reaction of organisms, such as plants, to the length of day or night. Photoperiodism is also the reaction of plants to the length of light and dark periods. Many flowering plants sense the length of night, a dark period, as a signal to flower. Each plant has a different photoperiod, or night length. When the plant senses the appropriate length of darkness, resulting in an appropriate length of daylight, it flowers. Flowering plants are classified as long-day plants or short-day plants. Long-day plants flower when the length of daylight exceeds the necessary photoperiod, and short-day plants flower when the day length is shorter than the necessary photoperiod. Long-day plants include carnations, clover, lettuce, wheat, and turnips. Short-day plants include cotton, rice, and sugar cane. Answer: they get shorter

Answer: What happens to the length of the days in the fall?

Question: Passage: The ductless endocrine glands are not to be confused with the body's exocrine system, whose glands release their secretions through ducts. Examples of exocrine glands include the sebaceous and sweat glands of the skin. As just noted, the pancreas also has an exocrine function: most of its cells secrete pancreatic juice through the pancreatic and accessory ducts to the lumen of the small intestine. Answer: glands

Answer:
"endocrine" and "exocrine" are two types of what?