The correct option is C Wouldn't break, packed
A sentence that begins with 'if' is a conditional. These sentences refer
to hypothetical situations, 'what could happen' and 'what we wish would
have happened'.
The given sentence is also a conditional. It's a
type 2 conditional, which means that the if-clause is a hypothetical
condition (packed the school bag more carefully) and the main clause is its probable result (the pencils would not break). In this type, the tenses used are:
main clause (present conditional) + if-clause (simple past)
Option C: The verb 'wouldn't break' presents a present conditional, 'would' refers to the condition, and 'packed' is in
simple past. It adheres to the requirement for type 2 conditional.
Hence C is the correct option.
Option A: 'Would break' is a present conditional (in the affirmative) and 'will' refers to the future tense. The former is wrong because the pencils would 'not' break if they had been packed carefully. The latter is wrong because the tense of the if-clause must be in the past.
Option B: 'Pack' refers to the present
action, but it should refer to the past.
Option D: 'Will not break' refers to the future and 'would pack' refers
to the present conditional. But, as mentioned above, the condition (if-clause)
cannot be a present conditional, leaving the result (main clause) in the future.
The meaning thus formed is ambiguous.
Hence options A, B and D are incorrect.