United States manufacturers currently produce most of the world's solar-power generators--most of which are exported to Europe. However, European manufacturers are emerging and probably will ultimately capture much of the European market. The United States government is funding initiatives intended to encourage use of solar power within the United States. If these initiatives succeed in increasing the demand for solar-power generators in the United States, United States manufacturers will probably maintain significant production levels, since __________.

Which of the following most logically completes the argument?

【选项】the efficiency of solar-power generators in converting energy from the Sun into electric power is not improving as fast as it once did