Given a scientific passage and an answer, generate a question for the given answer.

[EX Q]: Passage: The menstrual cycle includes events that take place in the ovary, such as ovulation. Answer: ovary
[EX A]: Ovulation takes place in what organ and is part of the menstrual cycle?

[EX Q]: Passage: 30.4 Leaves Leaves are the main site of photosynthesis. A typical leaf consists of a lamina (the broad part of the leaf, also called the blade) and a petiole (the stalk that attaches the leaf to a stem). The arrangement of leaves on a stem, known as phyllotaxy, enables maximum exposure to sunlight. Each plant species has a characteristic leaf arrangement and form. The pattern of leaf arrangement may be alternate, opposite, or spiral, while leaf form may be simple or compound. Leaf tissue consists of the epidermis, which forms the outermost cell layer, and mesophyll and vascular tissue, which make up the inner portion of the leaf. In some plant species, leaf form is modified to form structures such as tendrils, spines, bud scales, and needles. Answer: leaf
[EX A]: What part of the plant is the main site of photosynthesis?

[EX Q]: Passage: Figure 20.33 The outer surface of the heart changes from positive to negative during depolarization. This wave of depolarization is spreading from the top of the heart and is represented by a vector pointing in the direction of the wave. This vector is a voltage (potential difference) vector. Three electrodes, labeled RA, LA, and LL, are placed on the patient. Each pair (called leads I, II, and III) measures a component of the depolarization vector and is graphed in an ECG. Answer: depolarization
[EX A]:
The outer surface of the heart changes from positive to negative during what?