黃金閱讀 Geologic History of Mediterranean - 英檢

對不起大家我想請問黃金閱讀的這一題

我實在看不懂這句話，也不懂為什麼第三題的選項是A

以下是題目:

Paragraph 3: With question such as these clearly before them, the scientists
aboard the Glomar Challenger processed to the Mediterranean to search for the
answers. On August 23, 1970, they recovered a sample. The sample consisted of
pebbles of gypsum and fragments of volcanic rock. Not a single pebble was
found that might have indicated that the pebbles came from the nearby
continent. In the days following, samples of solid gypsum were repeatedly
brought on deck as drilling operations penetrated the seafloor. Furthermore,
the gypsum was found to possess peculiarities of composition and structure
that suggested it had formed on desert flats. Sediment above and below the
gypsum layer contained tiny marine fossils, indicating open-ocean conditions.
As they drilled into the central and deepest part of the Mediterranean basin,
the scientists took solid, shiny, crystalline salt from the core barrel.
Interbedded with the salt were thin layers of what appeared to be windblown
silt.


3．What does the author imply by saying “Not a single pebble was found that
might have indicated that the pebbles came from the nearby continent”?
ˇThe most obvious explanation for the origin of the pebbles was not
supported by the evidence.
○The geologists did not find as many pebbles as they expected.
○The geologists were looking for a particular kind of pebble.
○The different pebbles could not have come from only one source.

我不知道為什麼要選A

應該說我不懂選項A中提到的"The most obvious explanation" 是指什麼?

而選項中提到的evidence又是什麼 @@~~

請強者幫我解惑 謝謝 :)

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