Cambridge Primary (1-6). Stage 3. Science. Workbook - Unit 2: Mixing materials - Question 35

Sofia, Marcus and Zara are filtering dirty water. They all make different predictions.
Sofia: “The water will come out clean.”
Marcus: “The water will still be very dirty when it comes out.”
Zara: “The water will be less dirty when it comes out.”
The picture shows what happened.

Was Sofia’s prediction correct? How do you know?