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:
| Episode | Broadcast date | Run time | Viewers (in millions) | Archive |
| --- | --- | --- | --- | --- |
| " Episode 1 " | 21March1970 | 24:33 | 7.1 | PAL 2" colour videotape |
| " Episode 2 " | 28March1970 | 24:39 | 7.6 | Chroma dot colour recovery |
| " Episode 3 " | 4April1970 | 24:38 | 8.0 | Chroma dot colour recovery |
| " Episode 4 " | 11April1970 | 24:37 | 9.3 | Chroma dot colour recovery |
| " Episode 5 " | 18April1970 | 24:17 | 7.1 | PAL D3 colour restoration |
| " Episode 6 " | 25April1970 | 24:31 | 6.9 | Chroma dot colour recovery |
| " Episode 7 " | 2May1970 | 24:32 | 6.4 | Chroma dot colour recovery |
Question:
What is the archive of the show that aired on 18april1970?
Answer:
PAL D3 colour restoration