OE

“Inveighing” (expressing disapproval; railing against) would fit, but inveigling (winning over by flattery) is a trap. The clues are that this is an action done “against” China's record and “already inclined to invective (insulting or harsh language).” Speculating is too neutral, and lauding (praising) is too positive. Needling (teasing or provoking) can be negative, but would be done to someone or to some group, not something that could be done “against China's record.”
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(i) _________against China's record on environmental protection has become a ubiquitous pastime at energy summits, especially among those already inclined to invective on such topics.

"especially among those already inclined to invective on such topics" indicates that we need a negative word for the blank, which is synonymous with pouring invective. The answer is ranting.
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