Production of hyperosmotic urine

What role does the proximal convoluted tubule (PCT) play in renal osmoregulation?

1: It actively transports salt to the interstitium, diluting the tubular fluid.
2: It performs iso-osmotic reabsorption, where filtrate osmolarity equals blood osmolarity.
3: It is impermeable to water, leading to increased tubular fluid osmolarity.
4: It responds to ADH by increasing water permeability.