Considering alternate suppliers is a form of?

C. Contract Management -------------

That would be "Risk Analysis" as part of your Project Risk Management.

Alternate vendors added to the pre-qualified ones would be required only in case the main suppliers fail to meet the PO in any way.

I don't think this would be value engineering since the value engineering mainly focuses cost cutting (without compromising the scope, quality or schedule etc.) and you already have short list various suppliers on the pre-qualified list and place the order on the best Valued supplier.

Although option (c) could be the cloesest answer, I believe that having an alternative supplier will be always part of the Risk Management and supply security. Risk analysis would be therefore, part of the Risk Management.

value engineering, but also category strategy and negotiation preparation ;)

I also go with Option C - Contract Managment

Thank you for the invitation. My answer is A

My Answer Option C- Contract Management.

Thank you. I seem correct answer is option A. Value engineering.

D seems to be the answer. By having alternative suppliers already imply that one is already thinking of the risks once the suppliers in contract failed or missed out on the set agreement and there should be something to fall back on to be able to meet this agreement with the customer.

Option C - Contract Management , obviously  .

In my opinion , the appropriate option is A