Which Is True About Service Level Agreements (SLAs)

Which is true about Service Level Agreements (SLAs) ?

A) They ensure that both the service desk and its customers understand their responsibilities, and they describe how service performance is to be measured.
B) They should be simple, one to two page documents. If not, customers and IT staff will not take the time to fully read and comprehend them.
C) They are typically used to measure the performance of a service desk; other measures are used to measure the performance of the entire IT department.
D) They typically do not measure IT service characteristics such as security or availability, as these characteristics are measured by the security and availability teams.