The decision to merge the two companies a risky move at best was met with mixed reactions from shareholders.
Correct: A
The phrase 'a risky move at best' is an emphatic, non-essential parenthetical element that provides additional information about the decision. Dashes are often used to set off such phrases for emphasis or a more abrupt break than commas. Option A correctly uses a pair of dashes to set off this non-essential information. While commas could also work, dashes provide stronger emphasis, aligning with ACT's consideration of stylistic choices.