This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

Ex Input:
Many applications of silicate glasses derive from their optical transparency, which gives rise to one of silicate glasses' primary uses as window panes. Glass will transmit, reflect and refract light; these qualities can be enhanced by cutting and polishing to make optical lenses, prisms, fine glassware, and optical fibers for high speed data transmission by light. Glass can be colored by adding metallic salts, and can also be painted and printed with vitreous enamels. These qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures. Because glass can be formed or molded into any shape, and also because it is a sterile product, it has been traditionally used for vessels: bowls, vases, bottles, jars and drinking glasses. In its most solid forms it has also been used for paperweights, marbles, and beads. When extruded as glass fiber and matted as glass wool in a way to trap air, it becomes a thermal insulating material, and when these glass fibers are embedded into an organic polymer plastic, they are a key structural reinforcement part of the composite material fiberglass. Some objects historically were so commonly made of silicate glass that they are simply called by the name of the material, such as drinking glasses and reading glasses.

Ex Output:
What ingredient makes glass colorful?


Ex Input:
Regular script typefaces are also commonly used, but not as common as Ming or sans-serif typefaces for body text. Regular script typefaces are often used to teach students Chinese characters, and often aim to match the standard forms of the region where they are meant to be used. Most typefaces in the Song dynasty were regular script typefaces which resembled a particular person's handwriting (e.g. the handwriting of Ouyang Xun, Yan Zhenqing, or Liu Gongquan), while most modern regular script typefaces tend toward anonymity and regularity.

Ex Output:
What are commonly used?


Ex Input:
The Melbourne rail network has its origins in privately built lines from the 1850s gold rush era, and today the suburban network consists of 209 suburban stations on 16 lines which radiate from the City Loop, a partially underground metro section of the network beneath the Central Business District (Hoddle Grid). Flinders Street Station is Melbourne's busiest railway station, and was the world's busiest passenger station in 1926. It remains a prominent Melbourne landmark and meeting place. The city has rail connections with regional Victorian cities, as well as direct interstate rail services to Sydney and Adelaide and beyond which depart from Melbourne's other major rail terminus, Southern Cross Station in Spencer Street. In the 2013–2014 financial year, the Melbourne rail network recorded 232.0 million passenger trips, the highest in its history. Many rail lines, along with dedicated lines and rail yards are also used for freight. The Overland to Adelaide departs Southern Cross twice a week, while the XPT to Sydney departs twice a day.

Ex Output:
How many lines does the Melbourne rail network have?