Which of the following statements are correct? a) interrupts can cause concurrency even on a single processor: if interrupts are enabled, kernel code can be stopped at any moment to run an interrupt handler instead b) if a spin-lock is used by an interrupt handler, a processor must never hold that lock with interrupts enabled c) deadlock may occur when multiple locks are needed and and two or more processes each hold a subset of the locks d) Code must never hold a lock for a long time. A. Only b, c, and d B. Only a and c C. Only a, b, and c D. Only b E. a