The correct option is
B Opened
When we are dealing with such questions it is important to read through the entire passage, find the general tense and use the same to fill in the blanks according to the context. In this passage, it is suitable to use the various forms of the past tense.
To fill blank [26] option B, 'opened', which is in the simple past tense, is the correct answer. We can be sure of this by noting that the sentence we are referring to is in the simple past tense form.
Option A is incorrect because it is in the past continuous form and the past continuous describes an action or event in a time before now, which began in the past and is still going on at the time of speaking. Since the action of the old man opening his eyes happened and finished in the past, using this option would be grammatically incorrect.
Option C is incorrect because it is in the simple present form and the sentence requires it to be in the past tense.
We use past perfect to talk about something that happened before another action in the past, which is usually expressed by the past simple. Since the sentence does not refer to any other action that happened in the past, using this tense to fill this specific blank would be grammatically incorrect. Hence option D is incorrect as well.