f. Among the four students Zhang, Wang, Ben, and Zhao, one of them did a good deed outside of school and received praise. After being questioned, Zhang said: "It was Li who did it," Wang said: "It was Zhang who did it," Li said: "What Wang said is not true," and Zhao said: "It wasn't me who did it." After investigation, only one of them is telling the truth. So, the student who received the praise is ( ).
(a) Zhang
(B) Wang
(C) Li
(D) Zhao
6. If Zhang did the good deed, then Wang and Zhao are correct,
If Wang did the good deed, then Li and Zhao are correct,
If Li did the good deed, then Zhang, Li, and Zhao are correct,
If Zhao did the good deed, then Li is correct,
$\because$ Only one person is correct, $\therefore$ the good deed was done by Zhao. Hence, the answer is (D).