instruction:
This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
question:
Passage: Returning to the basic concept of current flows in a conductor, consider what happens if a half-wave dipole is not connected to a feed point, but instead shorted out. Electrically this forms a single 1⁄2-wavelength element. But the overall current pattern is the same; the current will be zero at the two ends, and reach a maximum in the center. Thus signals near the design frequency will continue to create a standing wave pattern. Any varying electrical current, like the standing wave in the element, will radiate a signal. In this case, aside from resistive losses in the element, the rebroadcast signal will be significantly similar to the original signal in both magnitude and shape. If this element is placed so its signal reaches the main dipole in-phase, it will reinforce the original signal, and increase the current in the dipole. Elements used in this way are known as passive elements. Question: What is a half wave dipole need to be coupled with in most instances?
answer:
feed point


question:
Passage: Ming government officials fought against each other, against fiscal collapse, and against a series of peasant rebellions. They were unable to capitalise on the Manchu succession dispute and installation of a minor as emperor. In April 1644, the capital at Beijing was sacked by a coalition of rebel forces led by Li Zicheng, a former minor Ming official, who established a short-lived Shun dynasty. The last Ming ruler, the Chongzhen Emperor, committed suicide when the city fell, marking the official end of the dynasty. Question: Who was Li Zicheng?
answer:
former minor Ming official


question:
Passage: Continental Portugal's 89,015 km2 (34,369 sq mi) territory is serviced by four international airports located near the principal cities of Lisbon, Porto, Faro and Beja. Lisbon's geographical position makes it a stopover for many foreign airlines at several airports within the country. The primary flag-carrier is TAP Portugal, although many other domestic airlines provide services within and without the country. The government decided to build a new airport outside Lisbon, in Alcochete, to replace Lisbon Portela Airport, though this plan has been stalled due to the austerity. Currently, the most important airports are in Lisbon, Porto, Faro, Funchal (Madeira), and Ponta Delgada (Azores), managed by the national airport authority group ANA – Aeroportos de Portugal. Question: How many national airports does Portugal have?
answer:

four