A: 555 is a CMOS555 time base circuit, while NE555 is a bipolar time base circuit. The minimum working voltage of the former is 3V, the static working current is only hundreds of μA, the maximum output current is less than 20mA, and the output voltage amplitude is very close to the supply voltage.
The minimum working voltage of NE555 is above 4.5V, the static working current is up to several mA, the maximum output current is up to 200mA, and the output voltage is about 1V lower than the supply voltage. Therefore, whether it can be replaced depends on the specific circuit.