The internal structure of the cell, including its organelles, is revealed under an electron microscope.
细胞内部结构，包括其细胞器，在电子显微镜下得以显现。
Dolphins use a form of biological sonar called echolocation, emitting clicks that bounce off nearby objects and return as echoes; by analyzing the timing and pattern of these echoes, dolphins can determine an object's size, shape, and even its internal density.
From a Central Ideas and Details question · Information and Ideas
Which choice best defines “internal”?
C — Located on the inside. “internal” means located on the inside.
Which word means “located on the inside”?
D — internal. “internal” means located on the inside.
internal — located on the inside. In Chinese: 内部的.
internal is pronounced /ɪnˈtɜrnəl/.
The internal structure of the cell, including its organelles, is revealed under an electron microscope. (细胞内部结构，包括其细胞器，在电子显微镜下得以显现。)
inner, interior, intrinsic — all close in meaning to internal (located on the inside).
external, outer — each the opposite of internal (located on the inside).
Yes. internal is on the SAT Prep Basic list — the everyday academic words the SAT assumes you already have. The Digital SAT does not test vocabulary in isolation; words like this one are tested through Words in Context questions, where you choose the word that completes a passage most logically and precisely.