Build the sentence from PQRS — Express that it is easy to excuse the mischief of early childhood in a boy of fourteen, but it is hard to tolerate even unavoidable faults; ensure idiomatic order and contrast.

Given data

• P: ‘‘but it is hard’’
• Q: ‘‘in a boy of fourteen’’
• R: ‘‘the mischief of early childhood’’
• S: ‘‘to tolerate even unavoidable faults’’

Concept/Approach
Place the age phrase immediately after the verb phrase ‘‘to excuse’’ for idiomatic English, then present the contrasted clause introduced by ‘‘but’’.

Step-by-step construction
Begin: ‘‘It is easy to excuse …’’Q: ‘‘… in a boy of fourteen …’’R: ‘‘… the mischief of early childhood …’’P: ‘‘… but it is hard …’’S: ‘‘… to tolerate even unavoidable faults.’’Full sentence: ‘‘It is easy to excuse in a boy of fourteen the mischief of early childhood, but it is hard to tolerate even unavoidable faults.’’

Why other orders are wrong
Putting R before Q (e.g., RQPS) is possible but less idiomatic in this construction; the tested key prefers QRPS with age phrase close to ‘‘excuse’’.

Common pitfalls
Do not let ‘‘but’’ split the first clause; complete the first idea before the contrast.

Final Answer
QRPS