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.

Example Input: Passage: Phycobilins are a third group of pigments found in cyanobacteria, and glaucophyte, red algal, and cryptophyte chloroplasts. Phycobilins come in all colors, though phycoerytherin is one of the pigments that makes many red algae red. Phycobilins often organize into relatively large protein complexes about 40 nanometers across called phycobilisomes. Like photosystem I and ATP synthase, phycobilisomes jut into the stroma, preventing thylakoid stacking in red algal chloroplasts. Cryptophyte chloroplasts and some cyanobacteria don't have their phycobilin pigments organized into phycobilisomes, and keep them in their thylakoid space instead. Question: What color is phycoerytherin?
Example Output: red

Example Input: Passage: Several references in Indian literature praise the knowledge of the Yavanas or the Greeks. The Mahabharata compliments them as "the all-knowing Yavanas" (sarvajnaa yavanaa) i.e. "The Yavanas, O king, are all-knowing; the Suras are particularly so. The mlecchas are wedded to the creations of their own fancy." and the creators of flying machines that are generally called vimanas. The "Brihat-Samhita" of the mathematician Varahamihira says: "The Greeks, though impure, must be honored since they were trained in sciences and therein, excelled others....." . Question: Who said "The Yavanas, O king, are all-knowing; the Suras are particularly so."?
Example Output: The Mahabharata

Example Input: Passage: Unlike the American GPS, Russian GLONASS, and European Galileo systems, which use medium Earth orbit satellites, BeiDou-1 uses satellites in geostationary orbit. This means that the system does not require a large constellation of satellites, but it also limits the coverage to areas on Earth where the satellites are visible. The area that can be serviced is from longitude 70E to 140E and from latitude 5N to 55N. A frequency of the system is 2491.75 MHz. Question: What is the frequency of the BeiDou-1 system?
Example Output:
2491.75 MHz