The prevailing distributed computing model of the current era is called ctiem servar computing.A（ ）is a solution in which the presentation, presentation logic,application logic,data manipulation and data layers are distributed between client PCs and one or more servers. A ( ) is a personal computer that does not have to be very powerful in terms of processor speed and memory because it only presents the interface to the user. A（ ）is a personal computer,notebook.computer,or workstation that is typically more powerful in terms of processor speed,memory,and storage capacity. A（ ）hosts one or more shamad database but also executes all database commands and services for information systems.A (n)（作答此空）hosts Internet or intranet web sites,it communicates with clients by returning to them documents and data.
A.Database server
B.Message server
C.Web server
D.Application server