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:
| Railroad (quantity) | Class | Road numbers | Builder | Build year |
| --- | --- | --- | --- | --- |
| Clinchfield Railroad (12 new, 6 secondhand) | E-1 | 650–657 | ALCO | 1942–1943 |
| Clinchfield Railroad (12 new, 6 secondhand) | E-2 | 660–663 | ALCO | 1947 |
| Clinchfield Railroad (12 new, 6 secondhand) | E-3 | 670–675 | ALCO | 1943 |
| Delaware and Hudson Railway (40) | J | 1500–1539 | ALCO | 1940–1946 |
| Denver and Rio Grande Western Railroad (21) | L-105 | 3700–3709 | Baldwin | 1938 |
| Denver and Rio Grande Western Railroad (21) | L-105 | 3710–3714 | Baldwin | 1942 |
| Denver and Rio Grande Western Railroad (21) | L-97 | 3800–3805 | ALCO | 1943 |
| Great Northern Railway (2 secondhand) | Z-6 | 4000–4001 | ALCO | 1937 |
| Northern Pacific Railway (47) | Z-6 | 5100–5120 | ALCO | 1936–1937 |
| Northern Pacific Railway (47) | Z-7 | 5121–5126 | ALCO | 1941 |
| Northern Pacific Railway (47) | Z-8 | 5130–5149 | ALCO | 1943–1944 |
| Spokane, Portland and Seattle Railway (8) | Z-6 | 900–905 | ALCO | 1937 |
| Spokane, Portland and Seattle Railway (8) | Z-8 | 910–911 | ALCO | 1944 |
| Union Pacific Railroad (105) | CSA-1 | 3900–3914 | ALCO | 1936 |
| Union Pacific Railroad (105) | CSA-2 | 3915–3939 | ALCO | 1937 |
| Union Pacific Railroad (105) | 4664-3 | 3950–3969 | ALCO | 1942 |
| Union Pacific Railroad (105) | 4664-4 | 3975–3999 | ALCO | 1943 |
| Union Pacific Railroad (105) | 4664-5 | 3930–3949 | ALCO | 1944 |
| Western Maryland Railway (12) | M-2 | 1201–1212 | Baldwin | 1940–1941 |
| Western Pacific Railroad (7) | M-100 | 401–407 | ALCO | 1938 |
Question:
what is the road numbers when the builder is alco, the railroad (quantity) is union pacific railroad (105) and the class is csa-2?
Answer:
3915–3939