Step 1: Context from the story.
This question refers to the chapter "Footprints Without Feet" where Griffin, a scientist, experimented with drugs that made his body invisible. The scientific explanation in the story says his body became transparent after swallowing certain rare drugs.
Step 2: Analyzing the options.
(A) red: Incorrect, nothing in the story mentions his body turning red.
(B) transparent: Correct — the drugs caused Griffin’s body to become transparent, making him invisible.
(C) blue: Incorrect, this is not in the text.
(D) flexible: Incorrect, his flexibility was not affected, only visibility changed.
Step 3: Conclusion.
The correct answer is (B) transparent.