Choose the part containing the error; if none, select ‘‘No error.’’ Sentence: The teacher promised that he will explain it if they come before school the following day.

Introduction / Context:
This question tests sequence of tenses in reported speech and conditional time clauses in formal English.

Given Data / Assumptions:

• Reporting verb: ‘‘promised’’ (past).
• Reported content includes a future reference and a condition.

Concept / Approach:
With a past reporting verb, backshift is normally applied: ‘‘will’’ → ‘‘would.’’ In the conditional clause referring to a future-in-the-past situation, simple present ‘‘come’’ may appear in direct speech, but in reported speech after a past reporting verb, ‘‘came’’ is typically used when the time reference is anchored in the past plan.

Step-by-Step Solution:
Identify backshift: ‘‘promised’’ → change ‘‘will’’ to ‘‘would.’’Optional refinement: ‘‘if they came’’ fits the past-time plan.Corrected core: ‘‘… that he would explain it …’’

Verification / Alternative check:
Compare direct speech: ‘‘He promised, ‘I will explain it if they come tomorrow.’ ’’ Reported: ‘‘He promised that he would explain it if they came the following day.’’

Why Other Options Are Wrong:
A and D are fine; C could be improved to ‘‘came’’ but the error the test targets is the failure to backshift ‘‘will’’ in B.

Common Pitfalls:
Keeping ‘‘will’’ after past reporting verbs; mixing direct and reported speech timelines.

Final Answer:
that he will explain it