Final answer:
To get up to a correct standing position faster, water skiers should focus on practicing balance and core strength exercises.
Step-by-step explanation:
The most appropriate activity to focus on during training to help a water skier get up to a correct standing position faster is practicing balance and core strength exercises.
Balance exercises, such as standing on one leg or using a balance board, can help improve stability and control when getting up from a kneeling or sitting position on the water skis.
Core strength exercises, such as planks or Russian twists, can help strengthen the muscles in the abdomen and lower back, which are important for maintaining a stable and upright position while skiing.