I didn’t quite follow him because he explained the theory _____that is too abstract for me.
---How often do you drop your e-pal a line?---_______, but usually once a week.
Our skin, if ______ to sunlight for a long time, can become darker.
_______ he met with the difficulty did he realize the importance of our help.
---How’s that? Who broke the glass?---Well, it ______ me. I was doing my homework the whole evening.
Don’t be discouraged. ______ things as they are and you will enjoy every day of your life.