Elson finished reading a storybook last week. He read an average of $19$ pages per day for the first four days of the week. He read an average of $25$ pages per day from Friday to Saturday. He did not read on Sunday. How many pages on average did Elson read per day throughout the entire week? 
选项为:A:$$21$$  B:$$20$$  C:$$19$$  D:$$18$$  E:$$17$$  请回答其中一个选项.