The line a tree whose hungry mouth is prest an example of iambic what?

The line "a tree whose hungry mouth is prest" is an example of iambic tetrameter.

Here's why:

* Iamb: An iamb is a metrical foot consisting of an unstressed syllable followed by a stressed syllable.

* Tetrameter: Tetrameter means there are four iambs in a line.

Let's break down the line:

* a (unstressed) TREE (stressed)

* whose (unstressed) HUN-gry (stressed)

* MOUTH (stressed) is (unstressed)

* PREST (stressed)

You can see that the line alternates between unstressed and stressed syllables, creating four iambic feet.