III. Cloze TestA. 16 – 20 題         Methane, the simplest alkane and a vital component of natural gas, is a potent greenhouse gasthat significantly contributes to the anthropogenic warming of the planet. It is naturally generated viavarious biochemical pathways, such as anaerobic decay of organic matter, as well as anthropogenicactivities, such as intensive animal husbandry and fossil fuel production. The atmosphericconcentration of methane has surged by over 150% since the pre-industrial era and now constitutesabout 20% of the total radiative forcing caused by greenhouse gases.         As reducing methane emissions has become a prime imperative for mitigating climate changeimpacts, several strategies ____16___, such as enhancing the efficiency of animal farming, cuttingdown waste generation in landfills, and trapping methane at oil and gas facilities. A new, burgeoningapproach to reduce methane emissions is the exploitation of methane as a renewable energy source,particularly in the form of biogas.         Biogas, a renewable, sustainable energy source, is derived by the anaerobic digestion of organicmaterials like animal waste, food scraps, and sewage sludge. This procedure generates a blend ofmethane and carbon dioxide, which can be processed to yield a purified fuel for heating, cooking, andelectricity production. Biogas presents several advantages ___17___ fossil fuels, such as itsecological sustainability, minimal carbon footprint, and ability to cut down methane emissions fromwaste disposal practices.          ___18___ its potential as a fuel source, methane can also be utilized as a feedstock formanufacturing an array of chemicals and materials. Methane, through various chemical reactions, canbe converted into diverse chemicals, such as methanol, which can be used as a fuel or as a buildingblock for producing other compounds. Methane can also be employed as a precursor for the synthesisof hydrogen, a pivotal component in numerous industrial processes.         Nevertheless, several challenges and hurdles have to be surmounted to realize the full potentialof methane as a fuel and feedstock. For instance, the production of biogas necessitates carefulmanagement of the anaerobic digestion process to guarantee that the methane is captured and notreleased into the atmosphere. Moreover, the purification and transportation of biogas are complex andcostly. Likewise, the conversion of methane into chemicals and materials ___19___ advanced,sophisticated technologies and procedures.          In summary, methane, the simplest hydrocarbon with vast potential as a fuel and feedstock, playsa crucial role in the climate change conundrum. However, its production and utilization should behandled with extreme caution to avoid unfavorable environmental effects, including the exacerbationof climate change. By investing in cutting-edge research and development and promoting sustainablepractices, we can optimize the benefits of methane ___20___ mitigating its disadvantages.
【題組】16.
(A) have proposed
(C) have been proposing
(B) are proposed
(D) have been proposed