This is the typical sequence of events:

1. The pilot finds a defect on the aircraft. They enter the details into the technical log.
2. The relevant work is done to fix or replace the broken part.
3. The maintenance release document is signed by the engineer to confirm that the work is complete and inspected.
4. The pilot now counter signs the maintenance release to accept the aircraft back into service.

In this question, 'the engineer leaves for a minute or two'. The engineer will inspect the work when it is complete and then sign the maintenance release to confirm all was done correctly. This allows the pilot to counter sign the paperwork and so accept the aircraft back into service.

Looking at the other answers:

'The Commander should ask the engineer to explain how he / she can sign the maintenance release when he / she was NOT involved in the work, nor did he / she watch it being carried out' --> INCORRECT as the engineer does NOT need to do the work, only inspect it on completion. The work could be done by another engineer or a technician.

'The Commander must ask the engineer to get the technician who completed the work to sign a maintenance release' --> INCORRECT. Technicians are NOT qualified to sign the maintenance release. They can carry out the work but only the engineer can sign this document.

'The Commander should reject the aircraft and ask for an independent check by another aircraft engineer' --> INCORRECT. Another engineer is NOT needed, the current engineer is qualified to check and certify the work that has been done.

Chapter 8 - Aeroplane Maintenance
8.8 Maintenance release

8.8.1 A maintenance release shall be completed and signed to certify that the maintenance work performed has been completed satisfactorily and in accordance with approved data and the procedures described in the maintenance organization’s procedures manual.

8.8.2 A maintenance release shall contain a certification including:

a) basic details of the maintenance carried out including detailed reference of the approved data used;
b) the date such maintenance was completed;
c) when applicable, the identity of the approved maintenance organization; and
d) the identity of the person or persons signing the release.

It is not sufficient to rely on oral contact between pilots and engineers when the aircraft arrives. Every malfunction, unreliable operation or damage including bird strikes observed by the crew must be reported in written and so does any work performed by the technicians, should it be repair or regular maintenance.

IMPORTANT NOTE: The correct option has been recently reviewed and updated according to recent feedback. The current correct option has been confirmed by several students.