Explanation:

- Calculate the initial total weight of 17 students:

$$

\text{Total weight} = 17 \times 56 = 952 \text{ kg}

$$

- Add the weights of the 3 new students:

$$

\text{Weights} = 57 + 62 + 68 = 187 \text{ kg}

$$

- Calculate the new total weight of all students:

$$

\text{New total weight} = 952 + 187 = 1139 \text{ kg}

$$

- Calculate the new average weight:

$$

\text{Average} = \frac{1139}{20} = 56.95 \text{ kg}

$$

- Evaluate the options:

- Option 1: 56.45 kg

- Option 2: 56.95 kg

- Option 3: 58.05 kg

- Option 4: 57.65 kg

Option 2, 56.95 kg, is the correct answer.