Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.
Since 1970, the United Nations has been celebrating April 22nd as Earth Day. It attracts millions of people worldwide to join in to promote public awareness of environmental protection.
A. Since 1970, the UNs has been celebrating April 22nd as Earth Day because it attracts millions of people worldwide to join in to promote public awareness of environmental protection.
B. The UNs has been celebrating April 22nd as Earth Day, which millions of people worldwide are attracted to join in it to promote public awareness of environmental protection.
C. Since 1970, the UNs has been celebrating April 22nd as Earth Day, which attracts millions of people worldwide to join in to promote public awareness of environmental protection.
D. Since 1970, the UNs has been celebrating April 22nd as Earth Day so that more people join in to promote public awareness of environmental protection.