Select the correct answer from the drop-down menu. Which supporting sentence would be best to add at the end of the first paragraph?
The following is a draft of a student essay. It may contain errors.

Save the Monarch
by Maribel Silva

(1) Over the past 25 years, the monarch butterfly population has drastically declined by 90%. (2) We need to become citizen scientists here at Wilson High School and do what we can to support and sustain the monarch population.

(3) It is important for us to understand how the problem started. (4) There are two principle causes for this decline: weather and habitat degradation. (5) Weather events such as tropical storms and droughts impact butterfly populations in general. (6) Habitat degradation, which is damage to or ruin of an animal or insect's natural habitat, plays an even larger part in population decline.
(7) What causes habitat degradation? (8) An invasive species that you may have heard of—humans. (9) In developing suburbia, people in North America are paving over and building on areas that were once open fields and pastures, manicuring their lawns, and using herbicides and pesticides in both gardens and large crops. (10) All these things have contributed to diminished access to the one thing that a monarch butterfly needs to continue the life cycle: milkweed.
(11) Unlike its name suggests, milkweed is not a weed. (12) Rather, it is a flowering perennial plant that comes in several varieties in North America. (13) Milkweed is the only thing that a monarch caterpillar will eat. (14) Therefore, an adult female monarch butterfly will only lay an egg on a milkweed plant, so that a growing caterpillar will have a food source until it becomes a butterfly.
(15) There is a common saying among butterfly conservationists: no milkweed, no monarchs. (16) Milkweed is disappearing in regions all across North America. (17) While existing ecosystems may be able to feed monarch butterflies through flowering plants that are not milkweed, they cannot support monarch caterpillars without milkweed.
(18) Around our school and in our neighborhoods, we need to create creature-friendly habitat gardens with native plants instead of merely ornamental ones. (19) Urban and suburban areas have ceased to be biologically diverse environments that support monarch butterflies. (20) Together, we can change that—one plant at a time—by intentionally cultivating milkweed that thrives in this area, along with other plants that support butterflies. (21) We will play a part in the important mission of saving the monarch.