Premise:
"Egghead Exam"
Hypothesis: Nerdy exam

yes

Premise:
"The Ramseys left their front door unlocked, and melting snow could have obscured footprints."
Hypothesis: The Ramseys left the house in a hurry, and forgot to lock the front door.

it is not possible to tell

Premise:
"Many of these wintry items are imported from the north of Portugal."
Hypothesis: These wintry items are specifically from Spain.
no