The best title for the text may be
A. Vaccinations: A Blessing or A Curse.
B. Principles of Vaccinations.
C. Vaccines: Methods and Implications.
D. A Miracle Cure Under Attack.
查看答案
The word "mandatory" most probably means ______.
A. compulsory
B. voluntary
C. recommendable
D. improved
微信支付 
支付宝支付