Correct Option (D)
Electrically operated machines are preferable to use.
Statements 3 ("Electrically operated machines are cheap to maintain") and 4 ("Electrically operated machines do not cause pollution") enumerate distinct advantages of electrically operated machines. These positive attributes-cost-effectiveness in maintenance and environmental benignity-collectively support the inference that such machines are desirable or preferable for use compared to alternatives that may lack these benefits.
Incorrect Options
Option (A): All machines are run by electric energy.
Statements 3 and 4 specifically refer to "electrically operated machines." This qualification implies that there exist other types of machines that are not electrically operated. If all machines were electric, the term "electrically operated" would be superfluous. Therefore, this inference is not supported by the given statements.
Option (B): There is no form of energy other than electricity.
Statement 2 affirms that electricity provides energy, but it does not claim exclusivity. The explicit mention of "electrically operated machines" in statements 3 and 4, by distinguishing them from other potential types, implicitly acknowledges the existence of machines powered by non-electric energy sources. Thus, this inference is unfounded.
Option (C): Most machines are operated on electric energy.
The provided statements offer no quantitative data or comparative statistics regarding the proportion of machines that operate on electric energy versus other energy forms. Consequently, an inference about whether "most" machines are electrically operated cannot be drawn from the given information.