1、灯具是文明的产物，人类通过有意识地固定火源，不断改进和演变这些用来固定火源的辅助设备，最终出现了专用照明的灯具。
A、正确
B、错误

单项选择题The author refers to 'external mechanisms' primarily in order toA.suggest that a biochemical analysis of dinosaur thermoregulation might be a waste of timeB.suggest that other means than warm-bloodedness may account for evidence of dinosaur thermoregulationC.explain why scientists are interested in looking for an absence of seasonal variations in oxygen 18 tracesD.suggest that metabolic rates, not warm-bloodedness, may have been the key factor in certain dinosaurs' survivalE.imply that other factors beside temperature may dictate the ratio of oxygen isotopes

单项选择题纳税期限是依法确定的纳税人()的期限。 A. 办理纳税登记 B. 办理税款预交 C. 据以计算应纳税额 D. 解缴税款