1. At the heart of a comer's coma lies a nucleus of solid material, typically no more than 10 kilometers across.
The word "heart" is closest in meaning to which of following?
(A) center
(B) edge
(C) tail
(D) beginning
2. The most graphic proof that the grand spectacle of a comet develops from a relatively small and inconspicuous chunk of ice and dust was the close-up image obtained in 1986 by the European Giotto probe of the nucleus of Halley's Comet.
The word "graphic" is closest in meaning to which of following?
(A) mathematical
(B) popular
(C) unusual
(D) vivid
3. As a comet's orbit brings it closer to the Sun, first the coma grows, then two distinct tails usually form.
The word "distinct" is closest in meaning to which of following?
(A) visible
(B) gaseous
(C) separate
(D) new
4. Pheromones are substances that serve as chemical signals between members of the same species.
The word "serve" is closest in meaning to which of following?
(A) improve
(B) function
(C) begin
(D) rely
5. Pheromones are the predominant medium of communication among insects (but rarely the sole method) . Some species have simple pheromone systems and produce only a few pheromones, but others produce many with various functions.
The word "sole" is closest in meaning to which of following?
(A) obvious
(B) best
(C) only
(D) final
