Answer from cs61c-cb (minh uyen nguyen 16765774) for Question 2
Because the "..." may mean that it branches far away, farther than can be represented in the 16 bits of the conditional branch instruction.  Since the program counter(PC) contains address of the current instruction, we can only branch within +/-(2^15) words of the current instruction if we use the PC as the register to be added to the address.