Placid means peaceful and tranquil.
The best synonym for placid would be C. peaceful.
Answer:
1) Statistics show that most vaccines are more than 90% effective in preventing diseases.
3) Polio and smallpox are two examples of diseases that have been eliminated through widespread vaccination
Explanation:
Sentence 1 and 3 are the ones stated more objectively and supported with facts.
In sentence 1, author supports the argument by referring to statistics and the effectiveness of vaccines in preventing diseases (90%).
In sentence 3, author supports the argument with facts that polio and smallpox have been eliminated by widespread use of vaccines.
However, sentences 2, 4, and 5 are very subjective and is based on author's opinion.
