When it comes to the long run in the production of goods and services, all inputs are variable.
For instance, if you needed to increase a factory's size in the short run, it would be very difficult which means that factory size is fixed in the short term. In the long term however, it becomes variable because there will be time to increase it.
In conclusion, the answer is option A.
Find out more on variable inputs at https://brainly.com/question/25753524.