Final answer:
The correct answer is losing 10 pounds in 2 weeks.
Step-by-step explanation:
The correct answer is: 1) Losing 10 pounds in 2 weeks.
All the other options mentioned are examples of general or long-term fitness goals. Running a marathon, increasing flexibility through yoga, and building muscle mass through weightlifting are all goals that can be achieved over a longer period of time with consistent effort and training. However, losing 10 pounds in 2 weeks is not a realistic or healthy goal, as it generally recommended to aim for a safe and gradual weight loss of 1-2 pounds per week.