Problem: I poured water from the bottle into the cup until *it* was empty.

Are "it" and "the bottle" the same?
Answer: yes

Problem: John was jogging through the park when he saw a man juggling watermelons. *He* was very impressed.

Are "He" and "John" the same?
Answer: yes

Problem: Jane knocked on the door, and Susan answered it. *She* invited her to come in.

Are "She" and "Jane" the same?
Answer: no

Problem: We went to the lake , because a shark had been seen at the ocean beach , so *it* was a safer place to swim.

Are "it" and "the ocean beach" the same?
Answer:
no