I'm afraid this painting is not by Picasso. It's only a copy and so it's _____.

At times the balance in nature is ______，resulting in a number of possibly unforeseen effects.

He is a strict but kind teacher, ___is always trying to make his classes __ and interesting . 

 There is an old proverb, “Love me, love my dog. ” But there is __________ wisdom in this: “Love me, love my book.” 

The strange grass never seen before is ______ to be a new plant.