As we know, penicillin became the greatest drug of the 20th century, ______ millions of lives.

__________ good exercise.

“ ______ as often as you can,” our English teacher often tells us, “ you will make rapid progress.”

 At the age of 29, Dave was a worker, ________ in a small apartment near Boston and ________ what to do about his future. 

       the course very difficult, she decided to move to a lower level.