【请教】 36套 exercise 20 一道阅读

Bianca999

Diamonds, an occasional component of rare igneous
rocks called lamproites and kimberlites, have never been
dated satisfactorily. However, some diamonds contain minute
inclusions of silicate minerals, commonly olivine, pyroxene,
and garnet. These minerals can be dated by radioactive decay
techniques because of the very small quantities of
radioactive trace elements they, in turn, contain. Usually, it is
possible to conclude that the inclusions are older than their
diamond hosts, but with little indication of the time interval
involved. Sometimes, however, the crystal form of the
silicate inclusions is observed to resemble more closely the
internal structure of diamond than that of other silicate
minerals. When present, the resemblance is regarded as
compelling evidence that the diamonds and inclusions are
truly cogenetic.      

1. The author implies that silicate inclusions were most  
   often formed
  (A) with small diamonds inside of them
  (B) with trace elements derived from their host  
    minerals
  (C) by the radioactive decay of rare igneous rocks  
  (D) at an earlier period than were their host  
    minerals
  (E) from the crystallization of rare igneous material
               

这题选D，对应的句子是 Usually, it is possible to conclude that the inclusions are older than their diamond hosts, but with little indication of the time interval involved.
虽然其它选项都不对，但这句话前面是possible to conclude，后面是but转折，而且是little否定，为什么还可以选D呢？
希望各位大神指教！感激不尽~~

zqszjmzy

我的理解，前半句意思是：inclusions are older than their diamond hosts，后半句意思是，（虽然早）但是没有显示早了多长时间。