As far as I can tell, the possibility that Neanderthals burned lichen/grass for heat/light does not exclude them burning it also for smoking food? Also, in support of answer choice A, it could be possible that the Neanderthals prioritized meat preservation over heat and light. The materials burned in the proximate fireplaces might have been used for food preservation even if its better for heat. It does seem to still weaken the argument.

the world thoroughly confused me - the teaching could theoretically be thorough but costs could still be reduced by spending more time teaching it.

I still don't understand how a well-designed place MUST be comfortable. It says that if it not-well designed it is uncomfortable, which makes sense. But couldn't it still be uncomfortable despite being well-designed?

I don't understand. The conclusion may not be correct if the data reported in the study is not correct. However, the conclusion is still logically drawn -the logic here acknowledges the conclusion stated is IF the study is correct.