The first four-legged animals to reach land were classified as blank

ichthyostega

Explanation:

First Four Legged Animals Inched Along.A reconstruction of the skeleton of the first four -legged land animal suggest that it didn't move too nimbly on land it either shuffled along or crept like an inchworm.360 million years ago, ichthtostega crawled out of the water onto land.

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.