Final answer:
The correct stream manipulator for exponential notation in C++ is 'scientific,' which is not listed amongst the given options. However, 'fixed' is mentioned, which is actually used for fixed-point notation, not exponential.
Step-by-step explanation:
The stream manipulator that forces cout to print floating-point values in exponential notation is not provided among the given options directly. However, the closest match, by inference and understanding the context of C++ standard library IO manipulators, would be fixed. The fixed manipulator is usually used for a contrary purpose, to force floating points to be displayed in fixed-point notation, whereas the exp is not an actual IO manipulator in C++. For exponential notation, one typically would use scientific as a stream manipulator, which is not listed. Based on the given options, one could argue that the question might contain a typo and exp is meant to represent scientific.