The verb form that correctly completes the sentence is:
- La semana pasada, mientras Arturo jugaba el fútbol, se cayó y se <u>lastimó</u> la pierna.
Explanation:
The Past Simple Tense uses the verbs in Preterite Form to mention the actions, in the <em>Spanish</em> case, the preterite forms for the verb <em>"lastimar"</em> are:
1. Me lastimé.
2. Te lastimé.
3. Se lastimó.
4. Nos lastimábamos.
In the case of the question, <em>how the noun is Arturo, who could be replaced by the object pronoun "se"</em> which uses the preterite form "lastimó".