Final answer:
The cause of Sarah's brother's death cannot be determined without more information.
Step-by-step explanation:
The likely cause of Sarah's brother's death cannot be determined without more information. The options provided - old age, malnutrition, a heart attack, and a car accident - are all possible causes of death, depending on the specific circumstances. For example, a heart attack could occur due to underlying health issues, while a car accident could be caused by reckless driving.