The correct option is A ful
When we add the suffix 'ful' to the word 'thought', we get the word 'thoughtful'. We can use it in a sentence like... 'He was attentive and thoughtful.' Thus, Option A is correct.
The other options are incorrect because the suffixes 'ment', 'ness' and 'tion' don't justifiably go with the word 'thought'.