ST is a Software Testing organization which utilizes a testing knowledge base.

The correct answer can be derived by applying the given rules to each case:

A is ST certified and has 12 years of testing experience, which is more than 10 years. Therefore, A does not match any of the rules and the result is unknown.

B is not ST certified and has 7 years of testing experience, which is between 5 and 10 years. Therefore, B matches rule 3 and the result is limited access.

C is not ST certified and has 3 years of testing experience, which is less than 5 years. Therefore, C does not match any of the rules and the result is unknown. Verified References: This question does not require any external references, as it is based on logical reasoning.