Fleming discovered penicillin almost by______.
He couldn’t ______ the fact that the money was found in his house.
Many scientists believe that the universe began with an enormous explosion called the “Big Bang”, ______ happened about 13.7 billion years ago.
—Don’t forget to visit me when you come to Beijing. —______.
—Your mother becomes more and more forgetful. —Yes. She searched for her cellphone for a whole day last Sunday but it ______ in her coat pocket the next day.
Would any one of you please tell me ______ to the railway station?