Kiyang Kwon. 2003. `That-t` Effects and the C-T Relation. Studies in Modern Grammar 32, 89-110. In this paper, we will consider the account of subject extraction out of `that`-clauses based on the split C strategy (Szczegielniak 1999) and the C-T Agree relation (Pesetsky and Torrego 2001) and point our their problems. According to Pesetsky and Torrego (2001), the C-T Agree relation is morphologically expressed in two ways: by merging `that` or merging the feature content of T (along with Agr) in C. However, we have assumed that if `do` in English is associated with a question, it is not independently attested as the realization of T but the realization of Q in c, serving as the interrogative morpheme. To obtain this argument, we have proposed the Q-feature of C as a property to determine the type of a clause. The Q-feature of C plays a role of distinguishing an interrogative C from a declarative C and can serve as a probe to seek the element with the interrogative morpheme, such as `-ni` in Korean.