Final answer:
The underlined verb 'threw' in the sentence 'Klete threw the ball to his sister.' is in the past tense.
Step-by-step explanation:
The sentence in question is "Klete threw the ball to his sister." The underlined verb in this sentence is 'threw.' To determine the verb form, we can look at the sentence structure and how the verb relates to time. 'Threw' is the simple past tense of 'throw,' which means that the action has been completed in the past. It does not have an auxiliary verb or an -ing, -ed, or -en ending, which would indicate other forms such as the present participle or past participle. Therefore, the correct form of the verb 'threw' in this sentence is past tense.