Directions (21-26) : Given below is a paragraph that has blank spaces. Corresponding to each blank, five options are given, out of which only one is appropriate. Choose the option that fits most suitably in the given blank making sentence grammatically and contextually correct. 

Gaseous refinery __________________(21) include hydrogen, fuel gas, ethane, propane, and butane. Most of the hydrogen is __________________(22) in refinery desulfurization facilities, which remove hydrogen sulfide from the gas stream and then separate that compound into elemental hydrogen and sulfur; small quantities of the hydrogen may be delivered to the refinery fuel system. Refinery fuel gas varies in composition but usually contains a __________________(23) amount of methane; it has a heating value similar to natural gas and is consumed in plant operations. The drawback is that periodic variability in heating value makes it __________________(24) for delivery to consumer gas systems. Ethane may be __________________(25) from the refinery fuel system for use as a petrochemical feedstock. In many cases, these operations take place in relatively remote regions and affect only those employed by the industry, so that little or no __________________(26) is attempted.