Question

when the 17th - century warship vasa was raised from stockholm harbor in 1961, conservators successfully stabilized its waterlogged oak hull using polyethylene glycol (peg) to prevent shrinkage. for decades, the ship appeared secure. in the early 2000s, however, chemist magnus sandström discovered that tons of sulfur—accumulated from bacteria while the ship lay on the seabed—were reacting with iron bolts and atmospheric oxygen to produce sulfuric acid. this acidification threatened to decompose the woods cellular structure. consequently, the museum had to expand its focus from physical stabilization to chemical neutralization, developing new treatments to arrest the corrosion.
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which choice best describes the overall structure of the text?
a it traces the construction history of a historic vessel, explains the environmental factors that led to its sinking, and describes the complex engineering methods used to recover it.
b it discusses the initial success of a preservation effort, details a subsequent chemical discovery that the preservation agents were degrading the artifact, and notes the revised strategy adopted to address that threat.
c it describes how a conservation project faced an unforeseen chemical problem years after the artifact appeared stable, prompting a shift in preservation methods.
d it argues that a specific conservation technique is obsolete, presents data comparing it to modern alternatives, and predicts the long - term stability of the artifact under the new protocols.

Explanation:

• Option A: The text does not discuss the construction history of the Vasa or the environmental factors leading to its sinking, so A is incorrect.
• Option B: The preservation agents (PEG) were not degrading the artifact; rather, sulfur from bacteria reacted with iron bolts and oxygen to produce sulfuric acid. So B's description of "preservation agents degrading the artifact" is wrong.
• Option C: The text first says the Vasa was stabilized (appeared secure), then a chemist discovered a chemical problem (sulfur reaction causing acidification threatening wood), and then the museum shifted from physical stabilization to chemical neutralization (new preservation methods). This matches the description in C.
• Option D: The text does not argue a conservation technique is obsolete, nor present data comparing techniques or predict long - term stability. So D is incorrect.

Answer:

C. It describes how a conservation project faced an unforeseen chemical problem years after the artifact appeared stable, prompting a shift in preservation methods.