Answer:
An outward shift in production possibility when resources are fixed is caused by improvement in technology which increases productivity.
Explanation:
A production possibility curve shows the different combination of two goods that can be produced using the fixed resources. Here, the two goods are grades in two courses and the fixed resource is study time.
The outward shift in PPF shows an increase in output level. Output level may increase because of several reasons.
Here, the resources i.e study time is assumed to be fixed. So, the increase in output level can be because of improvement in technology or in human capital which further helps in increasing productivity.