instruction:
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.
question:
The two largest metropolitan areas have subway systems: Lisbon Metro and Metro Sul do Tejo in the Lisbon Metropolitan Area and Porto Metro in the Porto Metropolitan Area, each with more than 35 km (22 mi) of lines. In Portugal, Lisbon tram services have been supplied by the Companhia de Carris de Ferro de Lisboa (Carris), for over a century. In Porto, a tram network, of which only a tourist line on the shores of the Douro remain, began construction on 12 September 1895 (a first for the Iberian Peninsula). All major cities and towns have their own local urban transport network, as well as taxi services.
answer:
What are the two subway systems in Portugal?


question:
Its knowledge and uses spread from China through the Middle East to medieval Europe in the 13th century, where the first water powered paper mills were built. Because of paper's introduction to the West through the city of Baghdad, it was first called bagdatikos. In the 19th century, industrial manufacture greatly lowered its cost, enabling mass exchange of information and contributing to significant cultural shifts. In 1844, the Canadian inventor Charles Fenerty and the German F. G. Keller independently developed processes for pulping wood fibres.
answer:
In what century did the papermaking process spread from China to Europe?


question:
One check on a magistrate's power was his collegiality. Each magisterial office would be held concurrently by at least two people. Another such check was provocatio. Provocatio was a primordial form of due process. It was a precursor to habeas corpus. If any magistrate tried to use the powers of the state against a citizen, that citizen could appeal the decision of the magistrate to a tribune. In addition, once a magistrate's one-year term of office expired, he would have to wait ten years before serving in that office again. This created problems for some consuls and praetors, and these magistrates would occasionally have their imperium extended. In effect, they would retain the powers of the office (as a promagistrate), without officially holding that office.
answer:
How long concurrently could an elected magistrate serve in office?