In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

[EX Q]: Which of the following is not a common shape for helicoids: large sheets, circular, or tube-like bridges?, Context: In the helical thylakoid model, grana consist of a stack of flattened circular granal thylakoids that resemble pancakes. Each granum can contain anywhere from two to a hundred thylakoids, though grana with 10–20 thylakoids are most common. Wrapped around the grana are helicoid stromal thylakoids, also known as frets or lamellar thylakoids. The helices ascend at an angle of 20–25°, connecting to each granal thylakoid at a bridge-like slit junction. The helicoids may extend as large sheets that link multiple grana, or narrow to tube-like bridges between grana. While different parts of the thylakoid system contain different membrane proteins, the thylakoid membranes are continuous and the thylakoid space they enclose form a single continuous labyrinth.
[EX A]: circular

[EX Q]: What distinguishes the district of Houston?, Context: Houston was incorporated in 1837 under the ward system of representation. The ward designation is the progenitor of the eleven current-day geographically oriented Houston City Council districts. Locations in Houston are generally classified as either being inside or outside the Interstate 610 Loop. The inside encompasses the central business district and many residential neighborhoods that predate World War II. More recently, high-density residential areas have been developed within the loop. The city's outlying areas, suburbs and enclaves are located outside of the loop. Beltway 8 encircles the city another 5 miles (8.0 km) farther out.
[EX A]: classified as either being inside or outside the Interstate 610 Loop

[EX Q]: Why are the mass transit systems elevated?, Context: Beneath the plain lies the Biscayne Aquifer, a natural underground source of fresh water that extends from southern Palm Beach County to Florida Bay, with its highest point peaking around the cities of Miami Springs and Hialeah. Most of the Miami metropolitan area obtains its drinking water from this aquifer. As a result of the aquifer, it is not possible to dig more than 15 to 20 ft (5 to 6 m) beneath the city without hitting water, which impedes underground construction, though some underground parking garages exist. For this reason, the mass transit systems in and around Miami are elevated or at-grade.[citation needed]
[EX A]:
it is not possible to dig more than 15 to 20 ft (5 to 6 m) beneath the city without hitting water