[单选题]The speaker who does not have specific words in his working vocabulary may be （ ） to explain or describe in a way that can be understood by his listeners.
A
obscure
B
difficult
C
impossible
D
unable
正确答案：D
题目解析
首先没有be obscure to do sth这种表达，所以排除A选项。B选项difficult和C选项impossible在作be ...... to do sth时前面的主语一般是it，而本题主语是名词及其定语从句，所以排除B、C。而be unable to do sth译为不能够做某事，符合句意。句意：那些在他的词语库里没有具体的词语的表达者将不可能以他的聆听者能听懂的方式解释或表达。
