20.What problem exists with doing the check that Prinn and Fegley have-|||-suggested?-|||-A.Few people have the necessary skills.-|||-B.Massachusetts Institute of Technology cannot do any more research.-|||-C.Recent acid rain has damaged the rock.-|||-D.Most rock layers have been disturbed since the Cretaceous era.

本题考查对地质研究方法局限性的理解。关键点在于岩层的稳定性：若岩层自白垩纪以来被扰动，原始特征可能被破坏，导致检测方法难以有效实施。需结合地质时间尺度与岩石保存条件分析选项。

选项分析

A. Few people have the necessary skills

错误。题目未提及技术门槛或人力资源限制，问题核心在于岩层本身的状态，而非检测能力。

B. Massachusetts Institute of Technology cannot do any more research

错误。选项与研究机构的限制无关，且题目未提供相关背景信息。

C. Recent acid rain has damaged the rock

错误。酸雨影响通常局限于地表岩石，而地质检测往往针对深层岩层。且酸雨是近期现象，与白垩纪（约1亿年前）时间跨度不符。

D. Most rock layers have been disturbed since the Cretaceous era

正确。白垩纪后经历多次地质运动（如板块碰撞、侵蚀），岩层可能被移动或改变，破坏原始特征，使检测方法难以准确反映历史环境。