【原创】There’s________ “u” and _______ “n” in the word “under”.

【原创】----What’s the matter, Mary? You look tired.
----I________ to prepare for the English test last night.

【原创】There are______ living things on the earth.

【原创】The man who is talking with Miss Wang ______ be Mr. Brown. He has gone to Paris.

【原创】Jack used to_______ to work, but he is used to________ to work now.