Explanation
BCDR planning tends to focus so much on the failing over of services in the case of a disaster that recovery back to primary hosting after the disaster is often overlooked. In many instances, this can be just as complex a process as failing over, if not more so. Availability of staff, capacity at the BCDR site, and change management processes are typically integral to BCDR plans and are common components of them.

A reservation guarantees to a cloud customer that they will have access to a minimal level of resources to run their systems, which will help mitigate against DoS attacks or systems that consume high levels of resources.
A reservation pertains to memory and CPU resources. Under the concept of a reservation, memory and CPU are the guaranteed resources, but storage and networking are not included even though they are core components of cloud computing. Software would be out of scope for a guarantee and doesn't really pertain to the concept.

Explanation
Transparency is the official process by which a cloud provider discloses insight and information into its configurations or operations to the appropriate audiences. Disclosure, openness, and documentation are all terms that sound similar to the correct answer, but none of them is the correct term in this case.

Explanation
A cloud customer utilizing proprietary APIs or services from one cloud provider that are unlikely to be available from another cloud provider will most negatively impact portability.