Unit 17. He was playing the guitar.

* 과거 진행 시제
- 현재 진행(~하는 중이다): am(1인칭) / is(3인칭 단수) / are(2인칭, 3인칭 복수) + -ing
- 과거 진행(~하는 중이었다): was(1인칭, 3인칭 단수) / were(2인칭, 3인칭 복수) + -ing
진행 시제에는 일반동사+ing 형태가 들어가는데, 이는 동사가 아님을 유의.
그래서 앞에 be 동사가 필요.
즉, 진행 시제는 be + -ing 형태.
be동사는 주어 인칭에 따라 형태가 바뀜.

I/he/she/it was taking/studying/having/cleaning ~.
we/you/they were taking/studying/having/cleaning ~.

과거 진행 시제는 과거 특정한 시점에 진행 중이었던 일을 말함.
예문)
I was sleeping at 3 o'clock yesterday.
I was taking a shower when Lisa called.
Ted was studying in London in 2001.
At 1 o'clock today, we were having lunch.
My parents were working in the same company when they first met.