a. Write one or more ARM instructions that will clear bits 20 to 25 inclusive in register RO. All the other bits of RO should remain unchanged. RO=AABBCCFF (5 points) b. Explain why you choose those instructions to meet the constrains given in the question? (5 points) c. Explain the step by step exception handling procedure in ARM7, when you switch the context from user mode to system mode. (5 points)