Explanation: Excessive coupling between an oscillator's output and an antenna means the antenna's varying impedance strongly influences the oscillator's resonant circuit. An antenna's impedance changes due to environmental factors, frequency shifts, and proximity to objects. When this variable load is highly coupled back, it directly affects the frequency-determining components of the oscillator. This causes the oscillator's frequency to drift ("frequency pulling") and its amplitude to fluctuate, leading to significant instability in both frequency and output power. * **A) The effect of cross-modulation of nearby frequencies:** Cross-modulation is a non-linear mixing phenomenon, typically in amplifiers or mixers, not the primary effect of an unstable oscillator due to antenna coupling. * **B) Instability of the oscillator and feedback op-amp:** While the oscillator becomes unstable, many RF oscillators don't use op-amps in their feedback path, making this answer unnecessarily specific and often incorrect for the general case. * **D) Frequency discrimination will be unstable:** Frequency discrimination is a process *downstream* from the oscillator (e.g., in an FM receiver). While an unstable oscillator would *cause problems* for a discriminator, "unstable frequency discrimination" is not the direct effect *on the oscillator itself*.