Explanation
Correct answer: A.
Choice A is the best answer. “However” logically signals that the information in this sentence—that envelope-shaped bags dominated the market—contrasts with the previous claim that these bags were impractical for carrying goods.
Why the other choices are wrong
Choice B
Choice B is incorrect because “for instance” illogically signals that the information in this sentence is an example supporting the previous claim that envelope-shaped bags were impractical for carrying goods. Instead, the sentence contrasts with the previous claim about the bags.
Choice C
Choice C is incorrect because “thus” illogically signals that the information in this sentence is a result of the previous claim that envelope-shaped bags were impractical for carrying goods. Instead, the sentence contrasts with the previous claim about the bags.
Choice D
Choice D is incorrect because “in other words” illogically signals that the information in this sentence is a paraphrase of the previous claim that envelope-shaped bags were impractical for carrying goods. Instead, the sentence contrasts with the previous claim about the bags.