Consider the following four-step assembly operation with quality problems:

• The first resource has a processing time of 5 minutes per unit and one employee doing the operation.
• The second resource has a processing time of 4 minutes per unit. It also has one employee doing the operation. However, this is a very delicate task and 80% of all products have to be scrapped after this step.
• Two workers are staffed for the third resource. No quality problems occur at this resource and the processing time is 20 minutes per unit.
• At the fourth and final resource, one operator handles the product. No quality problems exist at this step and the processing time is 12 minutes per unit.

Where in the process is the bottleneck?