题目

Beautiful pictures of mountains and forests, clear skies, flying birds, wild animals, silly faces — you can find them all in one place. 46  ? On a postcard! Have people always sent postcards? No! Before postcards, people  47 sealed (密封的) letters.The 48  for the first decorated (装饰的) postcard came to John P. Charlton in 1861. He thought a simple card  49 a border would be a great way to send a note. Then in the late 1800s, postcards which had pictures on them 50  . By law, people had to write their note on the front—on the picture! The back was 51 for the address. SeThere are ________ minutes in an hour, and ________ hours in a day. (　　)A.six; twentyB.sixty; twenty-fourC.twenty-four; four