Correct option is A
The upper cutoff frequency in a MOSFET amplifier is primarily limited by the parasitic (junction) capacitances inherent in the device's structure. These internal capacitances form low-pass filters with the circuit's resistances, causing the amplifier's gain to roll off as the frequency increases.
Key parasitic capacitances include:
Gate-to-Source Capacitance (Cgs).
Gate-to-Drain Capacitance (Cgd).
Drain-to-Source Capacitance (Cds).
