11) All multivibrators are level triggered. 12) A pulse-triggered flip-flop is identified by a bubble on its Q output terminal. 13) The 555 timer has three basic operating modes: monostable, bistable, and astable. 14) All multivibrators require feedback. 15) Shift register counters often include reset logic circuits to be cleared if the count is reached. 16) Parallel-in, parallel-out registers have parallel input and output buses. 17) Bidirectional shift registers can shift data either right or left. 18) Once an up/down counter begins its count sequence, it cannot be reversed. 19) The dot extension .CLK is used to indicate that the register device is a clocked FF. 20) A Moore state machine does not have a clock input.