A. grater
The correct answer is grater, but the correct spelling should be greater.

B. entertain
The correct answer is entertain. However, in the context of the sentence, it seems like entertain might be fine depending on context.

There have been a gradual decrease in the price of computers.
The underlined part that needs correction is:
A. have → should be has because "decrease" is singular.
Correct sentence: There has been a gradual decrease in the price of computers.

I'm thirsty, but I cannot find any glass to drink water.
The underlined part that needs correction is:
C. glass → should be glasses because you typically use the plural form when talking about drinking vessels in this context.
Correct sentence: I'm thirsty, but I cannot find any glasses to drink water.

Though Kate is always busy, she keeps to practice the violin regularly.
The underlined part that needs correction is:
C. to practice → should be practicing.
Correct sentence: Though Kate is always busy, she keeps practicing the violin regularly.

Question 28:
The Seven Wonders of the Ancient World include:
A. the pyramids
Correct answer: A. the pyramids

Question 29:
According to the passage, money for protecting our heritages may be provided by:
B. the World Heritage Fund
Correct answer: B. the World Heritage Fund

Question 30:
The underlined word "they" in the second paragraph refers to:
B. experts
Correct answer: B. experts

Question 31:
Which of the following statements is TRUE?
C. More places will be added to the UNESCO's list
Correct answer: C. More places will be added to the UNESCO's list

Question 32:
What would be the best title for this passage?
C. The Growing List of Wonders of the World
Correct answer: C. The Growing List of Wonders of the World

Question 33:
I suggested Jeff finish his test within the time allowed.

Question 34:
In order not to be disturbed, I closed the door.

Question 35:
Except Yumiko asks her counselor for advice, he can't help her.

Question 36:
Many people think that the Japanese eat with their eyes.

Question 37:
The exam isn't as difficult as we thought before.
The exam is easier than we thought before.

Question 38:
I never drank coffee when I lived in Spain.
I didn't use to drink coffee when I lived in Spain.

Question 39:
The cream is rather thick. It is ready to use.
The cream is so thick that it is ready to use.

Question 40:
We are trying harder so that our handicrafts can stay equal with theirs.
We are trying harder to keep up with theirs.