Disposal

Joan has traded in a non-current asset The entries in her journal include
Dr Non-current assets at cost
Cr Asset disposal
What aspect of the transaction is recorded by this entry?

a. Cash proceeds from disposal of the old non-current asset
b. Cash payment for purchase of the new non-current asset
C. Transfer of the original cost of the old non-current asset on disposal
d. Trade in value of the old non-current asset

I think D. Please help.