A system comprising a user equipment - UE - and a base station, in which: the user equipment comprises: a receiver (901, 905) configured to receive downlink data transmitted by the base station via downlink component carriers including a secondary component carrier; and a first circuit (903, 906) configured to select uplink resources from available resources for transmitting response signals obtained by decoding the received downlink data and selecting corresponding modulation symbols by using a mapping relation between a state of the response signals and the selected resources and the modulation symbols according to the state of the response signals; wherein the available resources include resources corresponding to a primary component carrier and extra resources allocated to the secondary component carrier by the base station; and wherein the mapping relation includes cases in which the resource corresponding to the response signal that is NACK/DTX is not selected, where NACK represents Negative Acknowledgement, and DTX represents Discontinuous Transmission, and when the response signals are all DTX, no resource is selected; and the base station comprises: a transmitter configured to transmit data to the user equipment by using the downlink secondary component carrier; and a second circuit (702, 801, 802) configured to select the extra resources from a first resource table if the number of transmission blocks for transmitting downlink data is 1, each of the elements in the first resource table including 1 resource, and to select the extra resources from a second resource table if the number of transmission blocks for transmitting downlink data is 2, each of the elements in the second resource table including 2 resources. a receiver (901, 905) configured to receive downlink data transmitted by the base station via downlink component carriers including a secondary component carrier; and a first circuit (903, 906) configured to select uplink resources from available resources for transmitting response signals obtained by decoding the received downlink data and selecting corresponding modulation symbols by using a mapping relation between a state of the response signals and the selected resources and the modulation symbols according to the state of the response signals; wherein the available resources include resources corresponding to a primary component carrier and extra resources allocated to the secondary component carrier by the base station; and wherein the mapping relation includes cases in which the resource corresponding to the response signal that is NACK/DTX is not selected, where NACK represents Negative Acknowledgement, and DTX represents Discontinuous Transmission, and when the response signals are all DTX, no resource is selected; and the base station comprises: a transmitter configured to transmit data to the user equipment by using the downlink secondary component carrier; and a second circuit (702, 801, 802) configured to select the extra resources from a first resource table if the number of transmission blocks for transmitting downlink data is 1, each of the elements in the first resource table including 1 resource, and to select the extra resources from a second resource table if the number of transmission blocks for transmitting downlink data is 2, each of the elements in the second resource table including 2 resources. a transmitter configured to transmit data to the user equipment by using the downlink secondary component carrier; and a second circuit (702, 801, 802) configured to select the extra resources from a first resource table if the number of transmission blocks for transmitting downlink data is 1, each of the elements in the first resource table including 1 resource, and to select the extra resources from a second resource table if the number of transmission blocks for transmitting downlink data is 2, each of the elements in the second resource table including 2 resources.