What event in act iv foreshadows macbeth's eventual downfall?

Macduff discovers Macbeth has murdered his family and vows to kill Macbeth himself.

Explanation:

Foreshadowing is a literary device in which a writer gives a hint of what is going to happen later in the story. Foreshadowing helps the reader develop expectations about the upcoming events of a story. Foreshadowing is also a useful device to create suspense and dramatic tension. This event shows that Macduff has discovered Macbeth's actions, and it hints towards an eventual conflict between Macduff and Macbeth.

comfortable

explanation:

one type of the adjectives is predicate adjective. a predicate adjective is an adjective which follows a linking verb and modifies or refers back to the main subject of that linking verb.

it usually is used just before the noun it modies.

here in this example:

'penguins seem comfortable in the coolest habitats', comfortable is the predicate adjective which follows the linking verb 'seem' and modifies the noun.