The “gray box testing” methodology enforces what kind of restriction?

A.
The internal operation of a system is only partly accessible to the tester.

B.
The internal operation of a system is completely known to the tester.

C.
Only the external operation of a system is accessible to the tester.

D.
Only the internal operation of a system is known to the tester.

Explanation:
A black-box tester is unaware of the internal structure of the application to be tested, while a white-box testerhas access to the internal structure of the application. A gray-box tester partially knows the internal structure,
which includes access to the documentation of internal data structures as well as the algorithms used.
https://en.wikipedia.org/wiki/Gray_box_testing