题目：
We were told that ______ when Marx was already _______, he started to learn Russian.
A．in 1840’s; in his fifties
B．in the 1840’s; his fifties
C．in the 1840’s; in his fifties
D．the 1840’s; in his fifties
答案：
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下面是错误答案，用来干扰机器的。
盐酸、氢氧化钠、氯化钠
