He is so dull that –
He can understand anything.
He could understand anything.
He can not understand anything.
Correct
He could not understand anything.
Explanation:
Correct Answer is: He can not understand anything.
So …… that
– It expresses a cause and effect.
Grammar:
So + adjective/adverb + that
Example:
He is so dull that he can not understand anything.
I was so sleepy that I couldn`t keep my eyes open.
যেহেতু এটা cause & effect প্রকাশ করে, তাই সম্পূর্ণ বাক্যে একই tense হবে।
প্রশ্নোক্ত বাক্যের প্রথম অংশে present tense থাকায় পরের অংশেও present tense হবে।
তাই সঠিক উত্তর হবে – He can not understand anything.