instruction:
Given a scientific passage and an answer, generate a question for the given answer.
question:
Passage: Pea plants are naturally self-pollinating. In self-pollination , pollen grains from anthers on one plant are transferred to stigmas of flowers on the same plant. Mendel was interested in the offspring of two different parent plants, so he had to prevent self-pollination. He removed the anthers from the flowers of some of the plants in his experiments. Then he pollinated them by hand with pollen from other parent plants of his choice. When pollen from one plant fertilizes another plant of the same species, it is called cross-pollination . The offspring that result from such a cross are called hybrids. Answer: cross-pollination
answer:
What is it called when pollen from one plant fertilizes another plant of the same species?

question:
Passage: Hydraulic car lifts also use fluid to transmit pressure and increase force. The lifts are used to raise cars, which are very heavy, so mechanics can work on them from underneath. Controls in airplanes use fluids to transmit pressure and increase force so a flick of a switch can raise or lower heavy landing gear. To see animations of hydraulic systems such as these, go to URLs:. Answer: hydraulic systems
answer:
What kind of systems use fluid to transmit pressure and increase force?

question:
Passage: A migraine is a more severe type of headache. It occurs when blood vessels in the head dilate, or expand. This may be triggered by certain foods, bright lights, weather changes, or other factors. People with migraines may also have nausea or other symptoms. Fortunately, migraines can often be relieved with prescription drugs. Answer: migraine
answer:
When blood vessels in the head dilate, what kind of severe headache can occur?