Among mammals, a herbivore has

Among mammals, a herbivore has flatter teeth than carnivore.

The mammals have four types of teeth which are incisors, canines, pre-molars and molars. 

• Incisors are sharp but flat and can be used to cut through the food easily.
• Canines are long and pointy and are used to tear through the food.
• Molars are very wide and flat which helps to crush and grind the food.
• Pre-Molars are used both as a canine and a molar which could be used to both tear and grind the food.

The mammals can be subdivided on the basis of their food habits - herbivores and carnivores. 

Herbivores are those who only consume plants. They have sharp but flat teeth, including incisors in the front and a molar in the back. They can hold, cut, and grind their food. Since they do not consume flesh, do they not need canines which helps in tearing flesh. Canines are a specialty of carnivores and omnivores since their diet includes flesh.

Hence, option B is the correct answer.