The correct answer is:
(a) Op-amp with low bias current
Explanation:
When working with high input source resistance, the input bias current of the op-amp becomes important because the high source resistance can cause a significant voltage drop across it, which can affect the performance of the circuit. To minimize this effect, you should choose an op-amp with a low input bias current. This reduces the voltage drop across the source resistance and ensures accurate signal amplification.
Why the other options are not as suitable:
(b) Op-amp with higher slew rate: While a high slew rate is important for fast signal changes, it is not directly related to dealing with high input source resistance. High slew rate is more relevant when dealing with high-frequency signals or large changes in voltage.
(c) Buffer or voltage follower: A buffer or voltage follower is indeed a good choice when you need to isolate the source from the rest of the circuit. However, this is more about impedance matching rather than directly addressing the high input resistance of the source.
(d) All of the mentioned: While the other options can be relevant in certain scenarios, (a) directly addresses the concern of high input source resistance, so it's the best choice for this specific situation.
Therefore, the most appropriate choice for high input source resistance is an op-amp with low bias current.