Will you be kind to tell me why lay has been used and not "LAY"

[Valentina T.]

Business English Lesson, Advanced Level

ESL/EFL Test #51 "Legal Expressions", question 7

Her parents are very strict and frequently ......... down the law about the way she behaves.

(a) lie
(b) lies
(c) lay
(d) lays

Business English Lesson, Advanced Level

ESL/EFL Test #51 "Legal Expressions", answer 7

Her parents are very strict and frequently lay down the law about the way she behaves.

Correct answer: (c) lay

Your answer was: incorrect
Her parents are very strict and frequently lays down the law about the way she behaves.
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Will you be kind to tell me why lay has been used and not "LAY", what I feel, the above sentence is in phural form.....please help

Valentina T.

[Conchita]

In the present simple, only the third person singular takes an 's':

I lay
you lay
he/she/it lays
we lay
you lay
they lay

[Mister Micawber]

.
...and 'parents lay'.
.
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Native English teacher at Mister Micawber's