Here are the sentences in passive voice and their corresponding active voice transformations:
Passive voice: "A ship carrying 350 tonnes of rice, water, tinned fish and other supplies arrived at Nias, Indonesia today, and we have already started distributing food to the people."
Active voice: "They have already started distributing food to the people after a ship carrying 350 tonnes of rice, water, tinned fish, and other supplies arrived at Nias, Indonesia today."
Passive voice: "In the early hours of Thursday, we managed to find a 13-year-old girl who was still alive."
Active voice: "In the early hours of Thursday, we managed to find a 13-year-old girl who still lived."
Note: The second sentence doesn't have a straightforward transformation as it describes a past action performed by "we." "Was still alive" could be understood as a passive construction created for emphasis, but it remains an assertion of her state. To keep the meaning, we can use "was alive" without changing the focus of the sentence to become more active. However, it’s not a classic example of passive voice.