Choose the best answer from (A), (B), (C) or (D), to complete sentence. I usually ____ in the river in the summer holidays.

The correct answer is: A. Swimming

The sentence is in the present simple tense, so the verb should be in the present participle form, which is “swimming”.

The other options are incorrect because:

• B. Swim is the infinitive form of the verb. It is used to talk about general actions or to give instructions. For example, “I like to swim” or “Can you swim?”
• C. Swam is the past tense form of the verb. It is used to talk about actions that happened in the past. For example, “I swam in the river yesterday” or “I have swum in the river many times.”
• D. Swims is the third person singular present tense form of the verb. It is used to talk about actions that a person or thing does regularly. For example, “The fish swims in the sea” or “My dog swims in the lake.”