3. At the moment they (to go) to the river for a swim. They usually (to go) to the river for a swim.

В данном задании необходимо раскрыть скобки, употребив глаголы в Present Continuous или Present Simple.

3. At the moment they (to go) to the river for a swim. They usually (to go) to the river for a swim.

В первом предложении речь идет о действии, происходящем в данный момент, поэтому используем Present Continuous. Во втором предложении речь идет о регулярно повторяющемся действии, поэтому используем Present Simple.

Следовательно, получим:

• At the moment they are going to the river for a swim.
• They usually go to the river for a swim.

Ответ: At the moment they are going to the river for a swim. They usually go to the river for a swim.