Which symbol is used to identify edge-triggered flip-flops? a triangle on the clock input. the letter e on the enable input. a bubble on the clock input. an inverted "l" on the output?

The triangle on the clock input is the symbol used to identify
edge-triggered flip-flops. An edge triggered flip flop changes its state either from 0 to 1 or vice versa at the positive edge (rising edge) or at the negative edge (falling edge) control input's clock pulse.