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.
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Question: The ecclesiastical structure of the Roman Empire survived the movements and invasions in the west mostly intact, but the papacy was little regarded, and few of the western bishops looked to the bishop of Rome for religious or political leadership. Many of the popes prior to 750 were more concerned with Byzantine affairs and eastern theological controversies. The register, or archived copies of the letters, of Pope Gregory the Great (pope 590604) survived, and of those more than 850 letters, the vast majority were concerned with affairs in Italy or Constantinople. The only part of Western Europe where the papacy had influence was Britain, where Gregory had sent the Gregorian mission in 597 to convert the Anglo-Saxons to Christianity. Irish missionaries were most active in Western Europe between the 5th and the 7th centuries, going first to England and Scotland and then on to the continent. Under such monks as Columba (d. 597) and Columbanus (d. 615), they founded monasteries, taught in Latin and Greek, and authored secular and religious works.

Answer: When did Gregory the Great become pope?

Question: In cpDNA, there are several A G deamination gradients. DNA becomes susceptible to deamination events when it is single stranded. When replication forks form, the strand not being copied is single stranded, and thus at risk for A G deamination. Therefore, gradients in deamination indicate that replication forks were most likely present and the direction that they initially opened (the highest gradient is most likely nearest the start site because it was single stranded for the longest amount of time). This mechanism is still the leading theory today; however, a second theory suggests that most cpDNA is actually linear and replicates through homologous recombination. It further contends that only a minority of the genetic material is kept in circular chromosomes while the rest is in branched, linear, or other complex structures.

Answer: What kind of gradients does cpDNA have?

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?