SASMO 2016 P2 Q6  Uncle John has a farm. His wife and his two sons are staying with him in the farm. They raise 10 cows and 20 chickens. How many total legs are there in the farm? 
选项为:A:$$60$$  B:$$80$$  C:$$86$$  D:$$88$$  E:$$120$$  请回答其中一个选项.