Although I majored in English, language _______ became a challenge when I set foot in the USA for the first time.
It is not always easy for the public to see _______ use a new invention can be of to human life.
He dressed up and went to the party as if ________.
After completing and signing it, please return the form to us in the envelope _______.
The book was written in 1946, _______ the education system has witnessed great changes.
He ______ be sitting at the gate, waiting for his lost son.