Given a scientific passage and an answer, generate a question for the given answer.

Ex Input:
Passage: 22.2.1 Lytic Cycle 1. Attachment: The virus binds to specific receptors on the host cell. Entry: There are two ways in which a virus can enter cells. Firstly, the virus can inject its nucleic acid into the host cell. Secondly, if a virus is contained in an envelope, the host cell can phagocytosise the entire virus particle into a vacuole. When the virus breaks out of the vacuole, it then releases its nucleic acid into the cell. Replication: The virus's nucleic acid instructs the host cell to replicate the virus's DNA or RNA. Assembly: New virus particles are assembled. Lysis and Release: The virus directs the production of an enzyme which damages the host cell wall, causing the host cell to swell and burst. The newly formed virus particles are now released. Answer: nucleic acid

Ex Output:
What does a virus inject into the host cell?

Ex Input:
Passage: Benzoic acid crystals in polarized light are pictured above. Benzoic acid is widely used as a food preservative, either as the carboxylic acid or as the sodium benzoate salt. This compound is most effective when added to acidic foods such as fruit juices and soft drinks. The major industrial source of benzoic acid is the partial oxidation of toluene with oxygen. The process is inexpensive and environmentally benign. Answer: benzoic acid

Ex Output:
What type of acid is often used as a preservative for acidic foods such as fruit juices?

Ex Input:
Passage: Solubility may increase or decrease with temperature; the magnitude of this temperature dependence varies widely among compounds. Notice in particular the curves for NH4NO3 and CaCl2. The dissolution of ammonium nitrate in water is endothermic (Hsoln = +25.7 kJ/mol), whereas the dissolution of calcium chloride is exothermic (Hsoln = 68.2 kJ/mol), yet Figure 13.9 "Solubilities of Several Inorganic and Organic Solids in Water as a Function of Temperature" shows that the solubility of both compounds increases sharply with increasing temperature. In fact, the magnitudes of the changes in both enthalpy and entropy for dissolution are temperature dependent. Because the solubility of a compound is ultimately determined by relatively small differences between large numbers, there is generally no good way to predict how the solubility will vary with temperature. The variation of solubility with temperature has been measured for a wide range of compounds, and the results are published in many standard reference books. Chemists are often able to use this information to separate the components of a mixture byfractional crystallization, the separation of compounds on the basis of their solubilities in a given solvent. For example, if we have a mixture of 150 g of sodium acetate (CH3CO2Na) and 50 g of KBr, we can separate the two compounds by dissolving the mixture in 100 g of water at 80C and then cooling the solution slowly to 0C. According to the temperature curves in Figure 13.9 "Solubilities of Several Inorganic and Organic Solids in Water as a Function of Temperature", both compounds dissolve in water at 80C, and all 50 g of KBr remains in solution at 0C. Only about 36 g of CH3CO2Na are soluble in 100 g of water at 0C, however, so approximately 114 g (150 g 36 g) of Saylor URL: http://www. saylor. org/books. Answer: fractional crystallization

Ex Output:
The separation of compounds on the basis of their solubilities in a given solvent is known as what?