Look at each option by how the grain sits inside it. Bhukari, PUSA bin and silo are all closed vessels or pits that are filled with loose grain, so they belong to the bulk storage family.
CAP, short for Cover and Plinth, works differently. A plinth is raised above ground level, filled bags of grain are stacked on it row by row, and the stack is wrapped in waterproof covers. This method is used widely by the Food Corporation of India for temporary open storage of bagged foodgrain.
\[\boxed{\text{CAP is the bag storage structure}}\]