6a. I lay my book on the table, but now I cannot find it.

6b. I laid my book on the table, but now I cannot find it.
I chose B. could you please explain?

2 answers

Thank you for using the Jiskha Homework Help forum. "I cnnot find it NOW" implies that you had already put the book on the table = past tense. Yes, it is B.
The parts of the verb to lie (meaning to recline) are:

lie, lay (past), have lain (past participle

The parts of the verb to lay (meaning to place or put) are:

lay, laid (past), have laid (past participle)

As Sra said, B is the correct answer.