问题
单项选择题
The gap between those at the lowest level and those at the highest level of income had increased ______, and is continuing to increase.
A. substantially
B. successfully
C. succinctly
D. sufficiently
答案
参考答案：A
解析： A选项：substantially根本地，充分地，符合句意。B选项：successfully成功地；C选项：succinctly简洁地，简便地；D选项：sufficiently十分地，都与句意不符，空格处意为“根本性地增大”。因此A选项为正确答案。