Though they have a (chemical composition similar to that of the common chrysoberyl), flawless emeralds are so rare that they are prized above any other gems except perfect rubies.
这个就是正确的不用改正,但我选的是similar chemical composition to the chrysoberyl's为什么就错了呢? 谁能帮忙解释一下!
参考资料:egregia cum laude from pre school DT