核心问题
“These look like machine stitches to me.” “No, they are all made ____.” A. with hand B. with hands C. by hand D. by hands(TOEFL) 答案为 C(by hand)，但我认为选项 A(with hand) 也是正确的。
词典解答
这里只能选C，而不能选A(with hand)。因为by hand是个固定短语，hand前不加冠词，意思是“手工地”(manually; using the hand or hands; without the use of machinery):
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The rug was obviously made by hand. (Whitford) 很明显, 这小地毯是人工编织的。
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Are your socks knitted by hand or machine-made? (ALD) 你的袜子是手工织的,还是
机器织的？
with 与 hand 搭配时必须使用冠词等限定词，并且不表示“手工地”“人工地”的意思。
He stood there, with his hands in his pockets. 他站在那里，两手插在衣袋里。