Using ABAP SQL, the select statement that selects the mat field on line #17 is:
SELECT mat FROM demo_sales_cds_so_i_ve…
This statement selects the mat field from the CDS view demo_sales_cds_so_i_ve, which is defined on line #1. The CDS view demo_sales_cds_so_i_ve is a projection view that projects the fields of the CDS view demo_sales_cds_so_i, which is defined on line #2. The CDS view demo_sales_cds_so_i is a join view that joins the fields of the database table demo_sales_so_i, which is defined on line #3, and the CDS view demo_sales_cds_material_ve, which is defined on line #4. The CDS view demo_sales_cds_material_ve is a value help view that provides value help for the material field of the database table demo_sales_so_i. The mat field is an alias for the material field of the database table demo_sales_so_i, which is defined on line #91.
The other options are not valid because:
A. SELECT mat FROM Material… is not valid because Material is not a valid data source in the given code. There is no CDS view or database table named Material.
C. SELECT mat FROM demo_sales_so_i… is not valid because demo_sales_so_i is not a valid data source in the given code. There is no CDS view named demo_sales_so_i, only a database table. To access a database table, the keyword TABLE must be used, such as SELECT mat FROM TABLE demo_sales_so_i…
D. SELECT mat FROM demo sales cds material ve… is not valid because demo sales cds material ve is not a valid data source in the given code. There is no CDS view or database table named demo sales cds material ve. The correct name of the CDS view is demo_sales_cds_material_ve, with underscores instead of spaces.
References: 1: Projection Views - ABAP Keyword Documentation