None of them can fight

A message appeared in Clark's mind.

"D-level zombie unique skill: Doubling!"

"The doubling can be applied to strength, speed, or weight, limited to oneself and cannot be attached to external objects. The current limits of doubling are: strength 50 times, speed 10 times, weight 50 times."

This strange information quickly disappeared, but it was deeply imprinted in Clark's mind, as if it were innate knowledge.

"I didn't expect my innate talent to be this. Looks pretty good!" Clark chuckled. 

After upgrading to a D-level zombie, his sensory abilities became even more acute. He could even vaguely sense the status of the zombies around him - those critically wounded and near death, and those still combat-capable, were all useful.

"What kind of monster are you?" Harris was witnessing this situation for the first time. Generally speaking, a zombie's level was predetermined, and there was no such thing as upgrading!