She stared at him ___________ she had seen a ghost.

Complete Sentence: She stared at him as though she had seen a ghost.

• 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.

• as if/as though (conjunction)
- 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.

অন্যদিকে,
- if (যদি),
- then (তখন),

Source:
1. Cambridge Dictionary.
2. Accessible Dictionary by Bangla Academy.