Here, the context refers to ability to complete an action. Thus, options B and D "is/can't" and "is/can" are incorrect as the auxiliary verb 'is' is incorrect.
"Can/can't" in option A is correct as 'but' indicates a contrast. Thus, one action can be done and the other can't be done.
"Can't/can't" in option C is incorrect as both indicate the ability to do the actions. However, 'but' indicates a contrast. Thus, one should indicate ability and the other should indicate inability.
Therefore, option A is correct.