The correct answer is SST because SST stands for serum separator tube, which is a type of blood collection tube that contains a gel separator. This gel separates the serum (the liquid part of the blood) from the other components, allowing for easy testing of various substances, including Alk Phosphatase. The other options mentioned (Green, Lavender, Red, Light Blue) are different types of blood collection tubes used for specific tests, but they are not suitable for testing Alk Phosphatase.