听力原文：M: Yes, we're lucky to have so much variety now. Though, as I said, these vegetables are not exactly new-- just new to us! People in other countries have been using them for years. Do you use any of them？
W: Well, I have tried one or two ... mainly to see if my son, Paul, would eat them. I'm very worried about him, as a matter of fact. He flatly refuses to eat vegetables...except potatoes.
M: But it's a very common problem. How old is your son？
W: He's almost ten. He's a strong boy and loves sports. And he always has plenty of energy...It's just that I'm concerned about the future.
M: But what is his diet like generally？ I mean, does he eat properly...apart from the lack of vegetables？
W: Well, he has a healthy appetite and he would eat chips forever...always covered in ketchup or tomato sauce.
M: Ah! That's also very common these days. All those sauces appeal to children because of the sugar content.
W: They don't have sugar in them, do they？
M: Ummm, I'm afraid they do!
W: Well, that explains it, I suppose. Paul does have a very sweet tooth. He'd do anything for sweets or ice cream. But what can I do to persuade him to eat vegetables？
M: Well, if he likes sauces, you can make wonderful, healthy salads these days from all sorts of different green leafy vegetables—different types of lettuce for vitamin B, spinach which provides vitamin A and iron, parsley and watercress which are also rich in iron...
W: Ummm ... I could try that, I suppose. I know he likes, what's it called, Thousand Island salad dressing ...
M: And I always recommend vegetable sticks to mothers who have your problem—you know, instead of letting him have chocolate bars or biscuits, get into the habit of giving him mw carrot sticks to nibble at.
W: That's a good suggestion.
Question : According to the man, why does tomato sauce appeal to children？
(23)

A. It is healthy.
B. It contains sugar.
C. It doesn't have sugar in them.
D. It is sour.