Choose the appropriate word from the options given to complete the following sentence.
The newest fibre optic cables that carry telephone calls are made of glass so______ that a piece 100 meters thick is clearer than a standard windowpane.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → transparent
Transparent means allowing light to pass through, so that objects behind can be seen distinctly. The sentence compares the glass with a windowpane and says that even a piece 100 metres thick is clearer than it, so the glass must be extremely transparent.
Example: Fresh mountain water is so transparent that you can see every pebble on the bed.
Why the Other Options are Incorrect?
Option 1: fragile — Incorrect. Fragile means easily broken or damaged; it is about strength, while the sentence is about how clear the glass is.
Example: Pack the fragile cups in plenty of paper.
Option 2: tangible — Incorrect. Tangible means that can be touched, or real and definite; it does not describe how well light passes through something.
Example: The new road has brought tangible benefits to the villagers.
Option 4: iridescent — Incorrect. Iridescent means showing bright rainbow colours that change with the angle of view; such glass would not be clearer than a windowpane.
Example: The soap bubble had an iridescent surface.