Complete the wildlife documentary script by dropping the correct present continuous verbs into the narrator's notes.

Look closely at the riverbank. The crocodiles are sleeping in the sun, while a brave little bird is cleaning their teeth.

The crocodiles are sleeping in the sun...

Because "crocodiles" is a plural subject (they), we use the auxiliary verb "are" with the -ing verb to describe what they are currently doing.

...while a brave little bird is cleaning their teeth.

Because "a brave little bird" is a singular subject (it), we use the auxiliary verb "is" with the -ing verb.