Hi Arabind
You can do the following setting
Alternate part 1 strategy 2 usage probability 100
Alternate part 2 strategy 2 usage probability nil
When you do the goods receipt according to strategy if complete stock is available against alternate part 1 it will considered first if stock is available with alternate part 2 not with part 1than at the time of goods receipt alternate part 2 is considered.
Try this if you have any further query than revert back.
Thanks & Regards
Sandeep Kumar Praharaj