What operator is used with cout to send data to standard output?

The operator used with cout to send data to standard output is the "<<" operator. This is also known as the "insertion" operator, as it inserts the data after the data already present in the output stream. The other options, such as +=, >>, and :, are not used in this context and therefore are incorrect. The += operator is used for addition assignment, the >> operator is used for input from the standard input, and the :: operator is used for scope resolution. Therefore, the correct answer is B.