题目

Frogs are animals that can live both in water and on land. There are more than 5,000 kinds of frogs on the earth. The earliest known frogs lived about 190 million years ago and the frogs today still look the same. Here are some fun things that you might not know about frogs. Enjoy! The Biggest and the Smallest Frogs Some frogs can be very big. The biggest kind of frog is the Goliath Frog in West Africa. Its body can be nearly 30cm long, about the size of a large cat. The Gold Frog and the Poison Frog are the smallest frogs in the world. They are less than 1cm long. Though the Poison Fro下列有关命题的说法中错误的是（ ）A．命题：“若是幂函数，则的图象不经过第四象限”的否命题是假命题B．设，则“”是“”的充要条件C．命题“且”的否定形式是“且”D．若为假命题，则均为假命题