There is an ongoing debate about the potentially harmful effects text messaging can have on people's grammar.
A. what
B. who
C. that
D. whose
网友回答
A. what
B. who
(答案→)C. that
D. whose
解析：句意：有关发短信对人们语法的潜在危害的辩论正在进行。先行词为the potentially harmful effects，在定语从句中作宾语，定语从句可还原为“text messaging can have potentially harmful effects on people's grammar”，且先行词指物，故选that。