11. (3 points) During the summer vacation, Xiaoming went to the park and met four classmates: Jia, Yi, Bing, and Ding. Xiaoming shook hands with all four classmates. Jia shook hands with 3 people, Yi shook hands with 2 people, and Bing shook hands with 1 person. How many people did Ding shake hands with? $\qquad$
【Answer】Solution: If everyone shakes hands with each other, then each person needs to shake hands 4 times,
Xiaoming shook hands with four classmates, including Ding and Bing;
Bing shook hands with 1 person, he only shook hands with Xiaoming, not with Jia;
Jia shook hands with 3 people, only one person didn't shake hands with him, so he only didn't shake hands with Bing, and he shook hands with Yi and Ding;
Yi shook hands with 2 people, he shook hands with Jia and Xiaoming, but not with Ding.
From this, we can see: Ding only shook hands with Jia and Xiaoming.
Therefore, the answer is: 2.