Final answer:
The slits between capillary endothelial cells allow small substances such as nutrients and oxygen to pass through, but not red blood cells or large plasma proteins. Thus, the correct answer is c) Nutrients and oxygen.
Step-by-step explanation:
The slits between capillary endothelial cells allow certain substances to pass through based on size and electric charge. Specifically, they permit the passage of small substances like nutrients and oxygen. Red blood cells and large plasma proteins are typically too large to pass through these slits. The fenestrations in the endothelial cells of capillaries prevent the filtration of blood cells and large proteins but allow smaller constituents, generally those less than 4 nm in size, to pass through. Considering these points, the correct answer to the question 'The slits between capillary endothelial cells allow ____ to pass through' would be c) Nutrients and oxygen. White blood cells can leave the bloodstream to enter tissues, but they typically do this by squeezing through the endothelial cell junctions in a process called diapedesis rather than passing through the fenestrations.