In the following question, two statements are given with some words in bold. Which of the following pairs of bold words must be interchanged to make both the sentences grammatically correct.

a. The Flint River water that was treated (A) improperly caused lead from ageing pipes to (B) leach into the water supply, leading to (C) protracted elevated levels of the heavy (D) metal neurotoxin.

b. The (E) acute withdrawal phase caused by the (F) reduction in intake of (G) opioids is often followed by a (H) extremely phase of depression and insomnia that can last for months.