Lewis drives from London to Brighton at an average speed of $$60\text{mph}$$. On the way back, he gets stuck in traffic and his average speed is only $$40\text{mph}$$. What is his average speed for the whole journey? 
选项为:A:$$55\text{mph}$$  B:$$50\text{mph}$$  C:$$48\text{mph}$$  D:$$45\text{mph}$$  E:Impossible to determine  请回答其中一个选项.