Option 1: 12 feet. This option suggests that a crab has 12 feet. However, this is incorrect. Crabs do not have 12 feet.

Option 2: 10 feet. This option suggests that a crab has 10 feet. However, this is incorrect. Crabs do not have 10 feet.

Option 3: 8 feet. This option suggests that a crab has 8 feet. This is the correct answer. Crabs have 8 legs, which are commonly referred to as "feet".

Option 4: 6 feet. This option suggests that a crab has 6 feet. However, this is incorrect. Crabs do not have 6 feet.

In conclusion, the correct answer is option 3, which states that a crab has 8 feet.