TPO2 The origins of cetaceans - 英檢

It should be obvious that cetaceans-whales, porpoises, and
dolpins-are mammals. They breathe through lungs, not through gills,
and give birth to live young. Their streamedlined bodied, the
absence of a hind legs, and the presence of a fluke and blowhole
cannot disguise their affinities with land dwelling mammals.
However, unlike the case of sea otters amd pinnipeds (seals, sea
lions, and walruses, whose limbs are functional both on land and
at sea), it is not easy to envision what the first whales looked
like. Extinct but already fully marine cetaceans are known from the
fossil record. How was the gap between a walking mammal and a
swimming whale bridged? Missing until recently were fossils clearly
intermediate, or transitional, between land mammals and cetaceans.

題目
1. In paragraph 1, what dose the author say about the presence of
a blowhole in cetaceans?

答案為(2)It cannot conceal the fact that cetaceans are mammals.

我選(4)It cannot yield clues about the origins of cetaceans.

請問為什麼答案不是(4)??

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