Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| PRR Class | Builder’s Model | Build date | Total produced | Wheel arrangement | Service | Power output |
| --- | --- | --- | --- | --- | --- | --- |
| GS4 | 44 Ton | 1948–1950 | 46.0 | B-B | Switcher | hp (kW) |
| GF25 | U25B | 1965 | 59.0 | B-B | Freight | hp (kW) |
| GF25a | U25C | 1965 | 20.0 | C-C | Freight | hp (kW) |
| GF28a | U28C | 1966 | 15.0 | C-C | Freight | hp (kW) |
| GF30a | U30C | 1967 | 5.0 | C-C | Freight | hp (kW) |
Question:
What was the model for PRR class of gf28a freight?
Answer:
U28C