Which ladder can be converted from a straight ladder to an A-frame configuration?

The combination ladder is designed to be versatile, allowing it to function both as a straight ladder and as an A-frame ladder. This adaptability makes it particularly useful in various firefighting and rescue scenarios. In the straight position, it can reach high places, while the A-frame configuration provides stability and support for tasks that require a shorter, more manageable height.

The other ladder types mentioned do not offer this dual functionality. The attic ladder is primarily designed for accessing attics and ceilings, and it does not convert to an A-frame. Fresno ladders are specialized and typically used for specific applications in firefighting but do not have the capability to be configured as an A-frame. Folding ladders may seem adaptable, but they usually do not provide the same structural integrity or height versatility as combination ladders when converting to an A-frame.

Thus, the combination ladder stands out for its multifunctionality in emergency situations, which is why it is the correct answer to the question.