Which of the following is the most specific group used to classify organisms?

The most specific group used to classification is genus and species.

Explanation:

Classifying a organisms into the species level we used hierarchical system. This system is known as taxonomic classification.The most specific group used to classification is genus and species.

Genus

To describe the generic name Genus is very useful way. When we use taxonomy to name an organism, the first part of its two-part name of an organism is determine by genus.

Species

The lowest and most strict level of classification of living things is species.The second part its two-part name of an organism is determin by species.

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.