TPO3 Architecture - 英檢

Paragraph 5:

▊ Modern architectural forms generally have three separate components
comparable to elements of the human body; a supporting skeleton or frame,
an outer skin enclosing the interior spaces, equipment, similar to the
body's vital organs and systems. ▊ The equipment includes plumbing,
electrical wiring, hot water, and air-conditioning. ▊ Of course in early
architecture─such as igloos and adobe structures─there was no such
equipment, and the skeleton and skin were often one. ▊


12. Look at the four squates (▊) that indicate where the following
sentence could be added to the passage.

However, some modern architectural designs, such as those using
folded plates of concreter or air-inflated structuresm are again
unifying skeleton and skin.

這題的正確解答是4。我有疑問的是，為什麼3不對呢？麻煩各位高手指點，謝謝！

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