The most obviously sarcastic phrase is, as it humorously contradicts the practical purpose of an umbrella by suggesting it is too delicate for contact with water.
The option (B) is correct.
The phrase from "Uses and Abuses of the Umbrella" that most clearly informs the reader that the author is being sarcastic. "...the umbrella is too fine, too delicate and lovely an article for water to be allowed to ruin it."
This statement qualifies as sarcasm because it contradicts the practical purpose of an umbrella, which is to protect against water. By stating the umbrella is too delicate for water, the author humorously inverts its actual use.