Mashaal Masha
When external forces are applied to common glass made from silicates, energy builds up around minuscule defects in the material, resulting in fractures. Recently, engineer Erkka Frankberg of Tampere University in Finland used the chemical ________ to make a glassy solid that can withstand higher strain than silicate glass can before fracturing.

Which choice completes the text so that it conforms to the conventions of Standard English?
Difficulty: Hard
A: 

compound, aluminum oxide

B: 

compound aluminum oxide,

C: 

compound, aluminum oxide,

D: 

compound aluminum oxide

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