Take another look at the sentence:

Jacob's physics notes were tucked in his book bag. A half-read copy of Moby-Dick served as a coaster for a glass of cold soda. An unopened trigonometry book was __________ on the desk. Although final exams were only two days away, Jacob decided to play another level of Tomb Raider, his favorite computer game.

The trigonometry book is resting on the desk. Thus, you need a form of lie. Since the sentence has a progressive verb, you need the present participle. Consult the table below or review the rules.

Infinitive Definition Simple Present Simple Past Past Participle Present Participle
to lay to put something down lay(s) laid laid laying
to lie to rest or recline lie(s) lay lain lying

Go to the next sentence.

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