This is a five-book collection, as seen below.
LESSON 16 THE PAST TENSE WITH 요 [AV-았/었어요 (2)]
LESSON 17 DESCRIBING EXISTENCE & POSSESSION [있다/없다(1)]
LESSON 18 DESCRIBING EXISTENCE & POSSESSION [있다/없다(2)]
LESSON 19 N에게(서) VS N에(서)
LESSON 20 NOT TO BE (N이/가+아니다)