How to do the grep the following in unix or AWK
===

I have a file some what like this

Start ---abcxyz

End ---- efg123

Ref ----2345

Slack---- lmnop

.....
......
and the above format repeats with other things in between next the "Start & Slack"

i want to grep the line from the file for "Start" "End" "Slack"
So how can we do in unix or using AWK.

-thanks 