An arch carries the thrust of weight to its _____(1)______. With a _____(2)______, the horizontal part of the structure supports all the weight above it.

An arch directs the thrust of its weight outward and downward to its supporting sides. In a post-and-lintel structure, the horizontal lintel supports the weight above it and transfers that load to the posts. So the blanks are “sides” and “post-and-lintel,” which is choice D.

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