Though great progress has been made in astronomy in the past fifty years, ______ still much that remains mysterious to astronomers _______ the universe, even the solar system [ ]

This is the house ______ they lived 5 years ago.

Hi, let’s go skating.— Sorry, I’m busy right now. I_____ in an application form for a new job.

To keep ______ with the rapid changes of society, the old man keeps the habit of reading newspapers every day.

Mum, I was wondering if you could lend me a fewdollars until I on Friday.