Although ancient tools were ___ preserved, enough have survived to allow us to demonstrate an occasionally interrupted but generally ___ progress through prehistory.
A needlessly
D documented
B rarely
E necessary
C noticeably
F continual
选BF
翻译：尽管保存下来的古代工具不多，但已经足够向我们展示一段偶尔被打断，总体上得以接续的史前工具发展概况。
首先注意让步/转折的指示词，既有although又有but，逻辑很好懂。
黄色提示部分，古代工具的保存状况尽管( )但是已经足够说明趋势了;
蓝色提示部分，偶尔被打断但总体上还是( )的进程。
用朴素的人类语感，两个空很好选，重点是读懂逻辑关系。
