下列句子中均有一处错误,请找出并改正.

下列句子中均有一处错误,请找出并改正.
1.Li Wei works harder than any student in his class.
A B C D
2.Shenzhen is one of the biggest city in China.
A B C D(C处包括the biggest)
3.If you don't know the meaning of the word,you can look up it in the dictionary.
A B C D(C处包括look up it)
4.Watering flowers are hard work,but I enjoy doing it.
A B C D
5.Tim was very exciting when he saw the computer.
A B C D

C other
D cities
C look it up
B is
B excited