The first textbooks __________ for teaching English as a foreign language came out in the 16th century.
The fact that smoking is harmful to health is____most smokers are quite aware of.
An example of them is fraud, a crime _______ money is stolen by cheating others.
Dr. Frank failed many times but he finally _____ to find a successful way to solve the problem.
---Where have you been? ---I got caught in traffic, otherwise I _______ here earlier.
—May I ask a question after class,sir? —____,but not during my lunch break.