Step 1 — Read the full sentence:
(a) The sound was taken up by another dog, and then another and another,
(b) till, borne on the wind which now sighed softly through the pass,
(c) a wild howling began, which seemed to come from all over the country,
(d) as far as the imagination could grasp them through the gloom of the night.
Step 2 — Check part (a):
"The sound was taken up by another dog, and then another and another," — this part is grammatically correct.
Step 3 — Check part (b):
"till, borne on the wind which now sighed softly through the pass," — the error lies here. The word "till" is incorrectly used. In this context, the correct word should be "until" or simply "then," because "till" does not fit smoothly with the rest of the sentence structure. This creates a grammatical inconsistency.
Step 4 — Check part (c):
"a wild howling began, which seemed to come from all over the country," — this part is grammatically correct.
Step 5 — Check part (d):
"as far as the imagination could grasp them through the gloom of the night." — this is also correct as it adds imagery to the sentence.
Step 6 — Correction:
Replace "till" with "until" for proper grammar.
Final Answer:
The correct option is (B) : b.