#1. Congratulations, you have answered correctly.
Exercise: According the Department of Energy, if we were to set up an area of solar cells equal to 0.25 the area currently covered by our roads, these cells could supply our entire (nations / nation's / nations') electrical needs.
Discussion: In general, to form the singular possessive of a noun, add 's.
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With a rear-facing child seat, the top of the seat and the (infants / infant's / infants') head will be in the deployment zone of the air bag.
#3. Congratulations, you have answered correctly.
Exercise: When you receive my (boss / bosses / boss's / boss' / bosses') memo requesting your participation, please respond to her that your job description, as written, will not allow you to perform that type of work.
Discussion: In general, to form the singular possessive of a noun, add 's. Occasionally, you will have a noun, such as "Moses" or "Mount St. Helens" with an s-sound ending such that addition of the possessive does not cause an extra s syllable in the pronunciation. In such unusual cases, the singular possessive is formed by the addition of an apostrophe. Note that "boss" is not one of these cases. The possessive form adds an extra syllable and therefore 's.
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This section explains the function of each technique and describes (its / it's / its') advantages and disadvantages.
#5. Congratulations, you have answered correctly.
Exercise: Since 1981, when the air traffic (controller's / controllers') strike occurred, the number of controllers decreased from 16,200 to 14,300 [Krasner, 1997].
Discussion: In general, to form the possessive of a plural noun, simply add an apostrophe to the plural form.
