28. The following code executes on an 8051 which has a 12 MHz clock. Which of the following is a reasonable guess of the execution time? 001B A290 22 MAIN: MOV C, P1.0 0010 8291 23 ANL 1 c. Pl.1 001F 9292 24 MOV P1.2, C 0021 80F8 25 SJMP MAIN a) 7 ns (b) 9 ns c) s d) 8 us e) 15 us f) 50 us 29. Which of the following commands should be used to return from an interrupt service routine? (a) RET b) LEAVE C) RET d) END 30. Which of the following address classifications does the command "MOVC A. @A+PC" belong? a) Register b) Direct Indirect d) Immediate e) Indexed f) Absolute