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see you can do one thing, make a voltage divider by PHOTO RESISTOR and one common resistor. Give supply to one terminal of photo resistor and connect other terminal to another simple resistor, now take this junction to drive one npn transitor. You shoul put current limit resistor betweent BASE and the junction of npn transitor. Connect buzzer between supply and collector of npn transistor. Ground emitter of same transistor.
Here as light falls on photo resistor the voltage at junction of this photo resistor and simple resistor will increase and it will ON the npn transitor.
Here the critical thing you have to take care of is selection of voltage divider.
This circuit will sound only when the intesity of light is increased. you must put variable resistor in seriese with photo resistor so that you can adjust level of intensity. and so on. there are so many practicles on this you have to do