12. The mid-term exam score statistics for Chinese, Mathematics, and English in a class are as follows: 18 students have at least one subject with an excellent grade; 9 students have an excellent grade in Chinese, 11 students have an excellent grade in Mathematics, and 8 students have an excellent grade in English; 5 students have an excellent grade in both Chinese and Mathematics, 3 students have an excellent grade in both Mathematics and English, and 4 students have an excellent grade in both Chinese and English. Ask:
(1) How many students have at least one excellent grade in Chinese or Mathematics?
(2) How many students have an excellent grade in all three subjects: Chinese, Mathematics, and English?
12. (1) 15 people; (2) 2 people.

Let the sets of students who excel in Chinese, Mathematics, and English be $A$, $B$, and $C$ respectively. From the problem, we have $|A|=9$, $|B|=11$, $|C|=8$, $|A \cap B|=5$, $|B \cap C|=3$, $|C \cap A|=4$, and $|A \cup B \cup C|=18$.
(1) $|A \cup B|=|A|+|B|-|A \cap B|=9+11-5=15$ (people);
(2) $|A \cap B \cap C|=|A \cup B \cup C|-|A|-|B|-|C|+|A \cap B|+|B \cap C|+$ $|C \cap A|=18-9-11-8+5+3+4=2$ (people).