He spoke as though _____________.

• As if/as though (conjunction) এর ব্যবহার: 
- as if/as though এর পূর্বে present indefinite tense থাকলে as if/as though এর পরে past indefinite হয়।
- be verb থাকলে সবসময় were হয়।

Example: He speaks as if he were mad.

• আবার, as if/as though এর পূর্বে Past indefinite tense থাকলে as if/as though এর পরে past perfect হয়।
Example: He spoke as though he had been mad.

তাই, Complete Sentence - He spoke as though he had known all the answers.