Dendrochronology, the study of tree-ring records to glean information about the past, is possible because each year a tree adds a new layer of wood between the existing wood and the bark. In temperate and subpolar climates, cells added at the growing season's start are large and thin-walled, but later the new cells that develop are smaller and thick-walled; the growing season is followed by a period of dormancy. When a tree trunk is viewed in cross section, a boundary line is normally visible between the small-celled wood added at the end of the growing season in the previous year and the large-celled spring wood of the following year's growing season. The annual growth pattern appears as a series of larger and larger rings. In wet years rings are broad; during drought years they are narrow, since the trees grow less. Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions.
However, trees that grew in areas with a steady supply of groundwater show little variation in ring width from year to year; these "complacent" rings tell nothing about changes in climate. And trees in extremely dry regions may go a year or two without adding any rings, thereby introducing uncertainties into the count. Certain species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again.
In the highlighted text, "uncertainties" refers to
dendrochronologists' failure to consider the prevalence of erratic weather patterns
inconsistencies introduced because of changes in methodology
some tree species' tendency to deviate from the norm
the lack of detectable variation in trees with complacent rings
the lack of perfect correlation between the number of a tree's rings and its age
A选项：“D"并没有考虑盛行的极端天气模式。文中确实提到了“D”不考虑极端天气模式。“trees in extremely dry regions may go a year or two without adding any rings”但是高亮词所在句的意思是指“年轮相似模式”可能出现的“不确定性”。而非考不考虑极端天气模式。
C选项：一些树木种类趋向于背离规范的种类。 文章提到过这个选项的内容“Certain species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again.”但是显然“uncertainty”指的不是这个。