In which caching technique does the ProxySG open multiple server connections to retrieve objects referenced on a web page before the client actually issues the requests for those objects? (Choose the best answer.)

In which caching technique does the ProxySG open multiple server connections to retrieve objects referenced on a web page before the client actually issues the requests for those objects? (Choose the best answer.)
A . Popularity contest
B . Cost-based deletion
C . Asynchronous adaptive refresh
D . Pipelining

Answer: D