Write a MIPS assembly code segment to bubble-sort three capital English letters stored at consecutive memory addresses 0x301, 0x302, and 0x303. Once sorted, the letters should be placed to the same memory locations in alphabetical order. If any of the characters in the given memory locations is not a capital English letter, then the character should be replaced by zero (0) and stored at the end of the sorted list in the memory. A subroutine should be called to perform any swap operation in the sorting algorithm. Use the MIPS register naming convention for passing arguments to and getting result from the subroutine. Show your subroutine code along with the main routine. Comment your code for full credit.