Meaning: 'Intense' means very strong or extreme, particularly in reference to heat or pressure.

Wrong options:

• Tremendously: Tremendously is an adverb that describes the extent of an action, but it cannot modify 'heat' directly as an adjective would.
• pretense: Pretense is a noun that refers to a false display or claim, which does not fit the context of describing heat and pressure.
• improperly: Improperly is an adverb that indicates something done incorrectly, which does not relate to the description of heat and pressure.
• behind: Behind is a preposition that indicates a position relative to something else, which does not fit as a descriptor for heat and pressure.

Correct answer: behind

Explanation: The word 'behind' serves as a preposition indicating the position of the glassy substance in relation to the atomic bomb test. It fits grammatically and contextually, as it suggests that the trinitite was left in the aftermath of the explosion.

Meaning: 'Behind' means at the back of or in the aftermath of something, indicating what remains after an event.

Wrong options:

• Tremendously: Tremendously is an adverb that does not fit as it cannot indicate a position or location in this context.
• pretense: Pretense is a noun that does not relate to the spatial context of the sentence and cannot indicate a position.
• improperly: Improperly is an adverb that describes the manner of an action, which does not fit the context of location.
• intense: Intense is an adjective that describes strength or degree, which does not fit as a preposition indicating position.

Correct answer: orderly

Explanation: The term 'orderly' is an adjective that describes the structure of quasicrystals, fitting grammatically as it modifies the noun 'structure.' It conveys that the arrangement of atoms in quasicrystals is systematic, aligning with the context of comparing it to normal crystals.

Meaning: 'Orderly' means arranged or organized in a systematic way, indicating a structured formation.

Wrong options:

• Tremendously: Tremendously is an adverb that cannot modify 'structure' and does not fit the context of describing the arrangement of matter.
• pretense: Pretense is a noun that does not relate to the description of structure and cannot serve as an adjective.
• improperly: Improperly is an adverb that indicates incorrectness, which does not fit as a descriptor for the structure of quasicrystals.
• intense: Intense is an adjective that describes strength or degree, which does not fit in describing the nature of the structure.

Correct answer: Previously

Explanation: The word 'Previously' is an adverb that indicates a time reference, fitting grammatically as it modifies the entire clause that follows. It establishes that the discovery of quasicrystals occurred before the current context of the sentence, providing a temporal relationship.

Meaning: 'Previously' means at an earlier time, indicating that the information about quasicrystals was known before the atomic bomb test.

Wrong options:

• Tremendously: Tremendously is an adverb that describes the extent of an action, which does not fit as a temporal marker in this context.
• pretense: Pretense is a noun that does not relate to the timing of events and cannot serve as an adverb.
• improperly: Improperly is an adverb that indicates incorrectness, which does not fit in establishing a time reference.
• orderly: Orderly is an adjective that describes arrangement, which does not fit as a temporal indicator.