Final answer:
The log-output variable in MySQL specifies the output destinations for the slow and General Query logs, which can include file or table destinations.
Step-by-step explanation:
The statement that is true about the log-output variable in MySQL is that it specifies output destinations for the slow and General Query logs. The log-output variable can be configured to determine where these logs should be written, such as a file or table. Option (a) is incorrect as log-output is not solely a static variable and can be set at runtime as well. Option (b) is not correct because the log-output variable itself does not enable or start the General Query Log; that is done by other variables such as 'general_log'. Option (c) is incorrect because the setting of the target location for binary logs is specified by the 'log_bin' variable and not log-output.