How is C the correct answer and not A?

I am also confused as to why the answer is C. Can someone please explain?

@Steph & @philip-blackmar, The argument tells us that the decline in energy consumption is due to decreased standards of living and changes the way people spend their time. (A) tells us that sales of portable heaters rose as families concentrated their winter activities in a limited number of rooms, which constitutes a change in the way people spend their time to decrease energy consumption as a portable heater consumes less energy than central heating. Hence, (A) supports the conclusion. (C) tells us that 39% of households decreased energy costs by having relatively inexpensive work done to improve the efficiency of their heating systems rather than by decreasing their standard of living or changing the way they spent their time. Since (C) provides an alternative explanation to a decline in energy consumption, it fails to support the argument's conclusion.

Reason why I didn't choose C - But isn't "by having relatively inexpensive work done" a reference to a decline of their standard of living? If their standard of living didn't cline, why would they have "inexpensive" work done?

Hi, if a project is always inexpensive, does that indicate a decline in living standards? I think people might simply be thrifty, or, more likely, if something is cheap, they don't feel the need to overpay for it.

Still don't understand why C is correct. E discusses water consumption regarding people took shorter showers, that's different from energy consumption, no? If this is a bizzaro question, wouldn't this justify that?

Showers absolutely would be included. Unless you take a cold shower, the hot water used in a shower is one of the largest uses of domestic power. C is correct because it actually undermines the conclusion. The conclusion is that people either had worse living standards or changed their time spend. C shows a different possibility from what the conclusion states: that people adapted by becoming more energy efficient.