Final answer:
Field agents can track parts and inventory, manage tasks, and navigate to task locations with a mobile device. However, approving contracts may not be possible from mobile due to the need for secure platforms, and calling customers might be restricted if it doesn't align with the mobile application's functions or company policies.
Step-by-step explanation:
A field agent using a mobile device can perform a variety of tasks that aid in their day-to-day operations while on the go. These tasks typically include options such as tracking parts and inventory (A), which allows for real-time updates and management of resources. Additionally, agents can manage tasks (C), which is crucial for scheduling and completing work assignments efficiently. With advancements in mobile technology, agents are now also able to navigate to task locations (E), using GPS and mapping apps to find the most efficient routes to their destinations.
However, there are some limitations to what can be done from a mobile device in the field. For instance, approving contracts (B) might require a more secure, possibly desktop-based, platform for legal or procedural reasons.
As for making calls to customers (D), although technically possible, it could arguably be included in the list if it falls outside the scope of the provided mobile application functionality or if there's a policy that mandates the use of other designated systems or protocols for customer interactions.