24.In the second paragraph, the word “thus” could be replaced by the word (A) when. (B) however. (C) if. (D) so.

28.The final sentence of the passage implies that the writer thinks (A) disease-carrying mosquitoes still pose a significant threat. (B) screens and insect repellent are ineffective protection against mosquitoes. (C) the threat of disease being transmitted by mosquitoes no longer exists in the U.S. (D) screens and insect repellent are the best protection against mosquitoes.