He is so dull that -

A He can understand anything.

B He could understand anything.

C He can not understand anything.

D He could not understand anything.

Correct Answer: Option C

so....that যুক্ত বাক্যে that এর পূর্বের clause টি যে tense এ থাকবে পরের clause টিও একই tense এ থাকবে