I am afraid that there is an impression that a verb is plural, when there is no s and a verb is singular when there is an s. This is erroneous. Used with helping verbs, they are only used in base form.
The basic structure of verbs in present tense is
Verb sing
Base form sing
Singular I person sing
Plural I person we sing
Singular II person you sing
Plural II person you sing
In all the above cases, the base form was simply used with the subject, whether singular or plural
Now let’s see how the structure changes with III person
III person singular (he, she, it) he sings, she sings and it sings, Tom sings etc
III plural (they) they sing
You can see the base form is used here( except in III person singular) and is acceptability called the plural verb.
Now when used with helping verb
(Singular) I can sing, you can sing, he can sing, she can sing and it can sing. Now we do not say - I can sings, you can sings, he can sings, she can sings and it can sings, just because the sub is singular
Now with helping verb (plural)
We can sing, you can sing, they can sing
And not we can sings, you can sings and they can sings.
In the given text, broaden and show are the base forms used with the helping verb may and not plural verbs.
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