Sentence rearrangement (PQRS) — Arrange the parts to complete a timeline sentence about the last expedition before exams starting in a month's time.

Given data

• Starter: 'It was to be'
• R: the last expedition
• P: before their school examination
• Q: which was due to start
• S: in a month's

Concept/Approach
State the complement noun phrase (R), then the time limiter (P), followed by a defining relative clause about the examination (Q), and complete with the time expression (S). We acknowledge the minor ellipsis in S ('in a month's [time]') as part of the source.

Step-by-step reconstruction
1) R → 'the last expedition' (what 'it' was to be).2) P → 'before their school examination' (temporal frame).3) Q → 'which was due to start' (relative clause referring to 'examination').4) S → 'in a month's' (idiomatic truncation for 'in a month's time').Sequence: RPQS.

Verification
Full sentence: 'It was to be the last expedition before their school examination which was due to start in a month's.'

Common pitfalls
Placing S before Q disrupts the relative clause; starting with P loses the complement immediately after the copula 'was to be'.

Final Answer
Correct order: RPQS.