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:
| Parameter | 1st stage | 2nd stage | 3rd stage | 4th stage |
| --- | --- | --- | --- | --- |
| Gross mass | 54,431kg | 462kg | 126kg | 42kg |
| Empty mass | 5,443kg | 231kg | 63kg | 21kg |
| Thrust | 667kN | 73kN | 20kN | 7kN |
| Isp | 248 s (2.43kN·s/kg) | 214 s (2.10kN·s/kg) | 214 s (2.10kN·s/kg) | 214 s (2.10kN·s/kg) |
| Burn time | 182 s | 6 s | 6 s | 6 s |
| Length | 18.28 m | 1.0 m | 1.0 m | 1.0 m |
| Diameter | 2.67 m | 1.0 m | 0.50 m | 0.30 m |
| Engine: | Rocketdyne S-3D | Eleven Sergents | Three Sergents | One Sergent |
| Propellant | LOX/RP-1 | Solid Fuel | Solid Fuel | Solid fuel |
Question:
What is the Parameter that has the third phase of 20kn?
Answer:
Thrust