---How long did it _____ you to work out the difficult maths problems?---I ______ about half an hour on it .
I used to to school by bike, but now I am used to to school.
There are some dangerous fishes in this river, and I’ve warned Jack here.
Chinese students often give small gifts or cards to their teachers on Teachers’ day to let them know _____.A.how great they areB.how great are theyC.what great they are
Tom found _____ difficult to learn chemistry well. A.it B.that C its
Our English teacher said _____ English well was very important. A.learn B.learning C.learned