Ashould follow a dependent clause when the dependent clause comes first in a sentence.
1. colon
2. comma
3. period
4. semicolon

this question is not school related. refrain from asking non school or academic related questions in the future.

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.