Correlative Conjunction is always used in pairs and denote equality, and show the relationship between ideas expressed in different parts of a sentence - and thus make the joining tighter and more emphatic. Some examples are either/or, neither/nor, and not only/but also.'Hardly' is followed by when and it is used to combine or rewrite sentences denoting two simultaneously past actions. In the given sentence it is inferred just at the moment he opened his eyes immediately saw her standing before me. These two past activities take place almost simultaneously. There is no real time difference between them. Thus Option B is correct. Option A can also be ruled out as 'Then' indicates 'in that case'. We use 'then' with 'if' to talk about cause and effect but it cannot be used in association with 'hardly' means 'scarcely' and it is used to combine or rewrite sentences denoting two simultaneously past actions.Option C is ruled out as 'than' introduces a comparison and is associated with comparatives and with words such as more, less, and fewer. 'Than' is also used with 'no sooner' to talk about something that happens immediately after something else. It is often used with the past perfect, The conjunction 'but' is used to suggest a contrast but it cannot be used along with 'hardly'.Thus Option D can be ruled out.