To identify a line from the passage that demonstrates a cause/effect text structure, look for a sentence that shows a clear relationship where one event (the cause) leads to another event (the effect). For example, a statement might explain how pollution (the cause) results in the formation of the Great Pacific Garbage Patch (the effect).
Since I don't have the exact passage, I can't provide a specific line for you. However, you should look for phrases indicating a reason and its impact or result. Lines starting with "as a result," "because of," "leads to," or "therefore" are typically good indicators of a cause/effect relationship.