Which of these groups of mammals is defined by having multicusped lower molars and a narrow pelvis?

a. allotheria

b. prototheria

c. theria

d. metatheria

e. eutheria

The correct answer will be option-A.

Explanation:

Allotheria is an extinct species of a mammalian group called marsupials which lived during the Mesozoic era.

The Allotheria can be easily distinguished by the few unique characteristics which were considered of non-placental mammals:

1. Presence of molariform teeth with longitudinal cusps in the lower portion of the mouth

2. Narrow pelvis which indicates that they used to give birth to young marsupials and used to feed them.

Thus, option-A is the correct answer.