(A) Starch
Carbohydrates not used immediately by plants are stored in the form of starch, which serves as the internal energy reserve.
Source: Life Processes, Section 5.2.1 Autotrophic Nutrition
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The passage directly states: "The carbohydrates which are not used immediately are stored in the form of starch, which serves as the internal energy reserve." This is a direct recall question — just identify 'starch' as the correct option. Glycogen (not starch) is the storage form in animals, so don't confuse the two.