1. A method of transmitting control information by a user equipment (UE) in a wireless communication system, the method comprising:detecting one or more physical downlink shared channels (PDSCHs) on a plurality of cells, wherein the plural cells are divided into a first cell set including a primary cell (PCell) and a first secondary cell (SCell) and a second cell set including one or more second SCells; and
transmitting hybrid automatic repeat request acknowledgement (HARQ-ACK) information through a physical uplink control channel (PUCCH) as feedback for the one or more PDSCHs,
wherein, when the one or more PDSCHs are detected only on the first cell set, the HARQ-ACK information includes HARQ-ACK responses only for the first cell set and is transmitted using a channel selection scheme and, when the one or more PDSCHs are detected at least on the second cell set, the HARQ-ACK information includes HARQ-ACK responses for both the first and second cell sets, and
wherein the channel selection scheme includes selecting one of PUCCH resources, and transmitting 2 bits corresponding to a set of HARQ-ACK responses for the PCell and the first SCell using the selected PUCCH resource.