What type of anchor would be appropriate for securing a unit with a bolt in a concrete floor?

A drop-in anchor is ideal for securing a unit with a bolt in a concrete floor because it is specifically designed for use in solid concrete. This type of anchor provides a strong and reliable hold due to its unique installation method, which allows it to expand as the bolt is tightened, creating a secure grip within the concrete.

Drop-in anchors are often used in applications where a flush finish is desired, making them suitable for securing equipment or fixtures without protrusions. They require a pre-drilled hole in the concrete, into which the anchor is inserted. Once the anchor is set, a bolt can be threaded into it to secure the unit.

In contrast, the other choices are typically not suitable for the same applications. Toggle bolts are meant for securing objects to hollow walls, nail-in anchors are used primarily for drywall or softer materials, and sleeve anchors are often used for both concrete and masonry but require installation in a different context. Thus, for securing a unit to a concrete floor, drop-in anchors deliver the necessary strength and stability.