help with the circuit diagram

[keron]

in the same  circuit please someone tell me(
http://www.zen22142.zen.co.uk/Circuits/Alarm/water_lev_alm.htm
why there is a 1Mohm resistor with 1uF cap inbetween the logic gates ,also the 47k and 10nF cap.please ?
                                what they are for and are they necesaary for normal functioning?if they are not there what can happen?

[audioguru]

The Cmos gates and the resistor and capacitor between them form Classic Cmos oscillators. The first gate gates each oscillator on and off.

EDIT:
The "piezo buzzer" is not a beeper with a built-in oscillator. It is a piezo speaker.