Single-use plastics have emerged (A) as one of the world's most buried (B) environmental threats (C), with vast amounts of waste pressing (D) in landfills or dumped (E) untreated in rivers and oceans.

The correct answer is B-D, meaning the words at positions (B) "buried" and (D) "pressing" must be interchanged with each other.

Let's first read the original sentence carefully:

"Single-use plastics have emerged (A) as one of the world's most buried (B) environmental threats (C), with vast amounts of waste pressing (D) in landfills or dumped (E) untreated in rivers and oceans."

Now let us identify what makes the sentence awkward or incorrect as it stands:

Problem with (B) — "buried":
The phrase "most buried environmental threats" is contextually wrong. The adjective "buried" does not collocate naturally with "environmental threats." We do not describe a threat as being "buried" — that does not convey urgency or significance.

Problem with (D) — "pressing":
The phrase "waste pressing in landfills" is also incorrect. The verb/adjective "pressing" in this context makes no logical sense — waste does not "press" in landfills as a standard environmental description.

The Fix — Swap B and D:
When we interchange "buried" (B) and "pressing" (D), the corrected sentence reads:

"Single-use plastics have emerged as one of the world's most pressing environmental threats, with vast amounts of waste buried in landfills or dumped untreated in rivers and oceans."

Why this is correct:

✅ "Most pressing environmental threats" — The word pressing means urgent, demanding immediate attention. It is a standard, well-established collocation in English (e.g., "pressing issue," "pressing concern," "pressing threat"). This perfectly describes how serious the plastic pollution crisis is.

✅ "Waste buried in landfills" — The word buried means placed under the ground or covered over. This is the standard way to describe how solid waste is disposed of in landfills (i.e., it is literally buried/dumped underground). This usage is factually accurate and linguistically sound.

All other options remain correct:
• emerged (A) — correct; plastics have "emerged" as a threat means they have risen/come to the forefront.
• threats (C) — correct as a noun.
• dumped (E) — correct; waste being "dumped untreated in rivers and oceans" is standard usage.

Therefore, the only interchange needed is B-D — swapping "buried" and "pressing" — to make the sentence both grammatically and contextually accurate.