Ⅳ. Complete the passage with proper words according to the Chinese given.
Students discuss the secrets of whales online.

Team Chat 4
Do you know anything about giant whales? I'm curious about your
ideas.
We know 1. there are many whales. They live from warm
southern waters to 2. 北方的 cold sea. The blue whale is the
largest.
As for the size, I agree with you. I had an 3. 争论 with my
friend last week. She thought dinosaurs were bigger.
Wait, their "songs" are so cool and different kinds of sounds travel
across oceans! My belief is that they use them to find friends. But why
they copy human speech is still 4. 未知的 ... Maybe they're
just curious?
I wish we have better research methods to learn more—there's so much
we don't 5. 完全地 understand! Like, how do they sleep with
one eye open? Also, did you know baby blue whales can drink up to 600
litres* of milk a day?
By learning about them, we keep these sea friends alive and happy.

Ⅳ. 1. that 2. northern 3. argument 4. unknown 5. fully