Problem: Please answer a question about the following article about Glass:
Addition of lead(II) oxide lowers melting point, lowers viscosity of the melt, and increases refractive index. Lead oxide also facilitates solubility of other metal oxides and is used in colored glasses. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glasses); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in vitreous enamels and glass solders. The high ionic radius of the Pb2+ ion renders it highly immobile in the matrix and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda-lime glass (108.5 vs 106.5 Ohmcm, DC at 250 C). For more details, see lead glass.
What makes glass melt at a lower temperature?
A: lead(II) oxide
Problem: Please answer a question about the following article about Slavs:
Conversely, some Slavs were assimilated into other populations. Although the majority continued south, attracted by the riches of the territory which would become Bulgaria, a few remained in the Carpathian basin and were ultimately assimilated into the Magyar or Romanian population. There is a large number of river names and other placenames of Slavic origin in Romania.[better source needed]
Majority of Slavs continued south to the riches of the territory that became what country?
A: Bulgaria
Problem: Please answer a question about the following article about Classical music:
The Medieval period includes music from after the fall of Rome to about 1400. Monophonic chant, also called plainsong or Gregorian chant, was the dominant form until about 1100. Polyphonic (multi-voiced) music developed from monophonic chant throughout the late Middle Ages and into the Renaissance, including the more complex voicings of motets.
What does Polyphonic mean?
A: multi-voiced
Problem: Please answer a question about the following article about Philosophy of space and time:
The example Leibniz uses involves two proposed universes situated in absolute space. The only discernible difference between them is that the latter is positioned five feet to the left of the first. The example is only possible if such a thing as absolute space exists. Such a situation, however, is not possible, according to Leibniz, for if it were, a universe's position in absolute space would have no sufficient reason, as it might very well have been anywhere else. Therefore, it contradicts the principle of sufficient reason, and there could exist two distinct universes that were in all ways indiscernible, thus contradicting the identity of indiscernibles.
Leibniz's example involves how many universes?
A:
two