1, because this is a single-supply operational amplifier circuit, and the single-supply operational amplifier circuit should have a virtual ground. R7 and R8 are divided to get half the power supply voltage, R9 is a current-limiting resistor, and the operating point of the operational amplifier only needs voltage. To understand this, we have to understand the internal circuit of operational amplifier, which is often called OP amplifier.

2. The input is not a filter, so C2 is a coupling capacitor and must be used in the feedback loop. Similar to the coupling capacitor in transistor amplification, C 1 acts as a filter capacitor in the circuit, which can be regarded as a low-pass filter, but actually it is an anti-interference capacitor.