HI, i am practicing for Salesforce developer 1.  I came across this question and the answer offered didnt make any sense to me.

The operation manager at a construction company uses a custom object called Machinery to manage the usage and maintenance of its cranes and other machinery. The manager wants to be able to assign machinery to different construction jobs, and track the dates and cost associated with each job. More than one piece of machinery can be assigned to one construction job. What should a developer do to meet these requirements?

1. Create a lookup field on the machinery object to the construction job object
2. Create a junction object with Master-Detail Relationship to both the machinery object and the construction job object.
3. Create a lookup field on the construction job object to the machinery object
4. Create a Master-Detail lookup field on the machinery object to the construction job object

The answer provided was n.3.  I would have gone with n.2.

Would you be able to help me with this and explain the answer to this by any chance

Many thanks