Learn to say what you are in the middle of doing with -는 중이다, and when to use -고 있다 instead.
By the end, you can build V-는 중이에요 / 중이었어요 / 중이라서 correctly, including ㄹ-stem verbs. You can also tell when -는 중이다 does not work and you need -고 있다 or the plain verb instead.
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