You design a SQL Server 2008 Reporting Services (SSRS) solution. You create a report by using Microsoft Visual Studio .NET 2008.
The report contains the following components:
A dataset named Customer that lists all active customers and their details. The dataset accepts no parameters. A dataset named SalesHistory that lists all sales transactions for a specified time period and accepts year and month as parameters.You need to ensure that a summary of sales transactions is displayed for each customer after the customer details.
Which component should you add to the report?

A.
List

B.
Table

C.
Matrix

D.
Subreport

Explanation:
Tip: "no parameters … to ensure that a summary" = "Subreport"

http://msdn.microsoft.com/en-us/library/ms160348(SQL.100).aspx
How to: Add a Subreport and Parameters (Reporting Services)
Add subreports to a report when you want to create a main report that is a container for multiple related reports. A subreport is a reference to another report. To relate the reports through data values (for example, to have multiple reports show data for the same customer), you must design a parameterized report (for example, a report that shows the details for a specific customer) as the subreport. When you add a subreport to the main report, you can specify parameters to pass to the subreport.
You can also add subreports to dynamic rows or columns in a table or matrix. When the main report is processed, the subreport is processed for each row. In this case, consider whether you can achieve the desired effect by using data regions or nested data regions.