Explanation
The correct ON condition that must be inserted in place of "???" is:
ON Sprojection.carrier_id=Z_Source2.carrier_id
This ON condition specifies the join condition between the CDS view Sprojection and the database table Z_Source2. The join condition is based on the field carrier_id, which is the primary key of both the CDS view and the database table. The ON condition ensures that only the records that have the same value for the carrier_id field are joined together1.
The other options are not valid ON conditions, because:
A: ON Z_Sourcel.camer_id = 7_Source2 carrier_id is not valid because Z_Sourcel and 7_Source2 are not valid data sources in the given code. There is no CDS view or database table named Z_Sourcel or
7_Source2. The correct names are Z_Source1 and Z_Source2. Moreover, the field camer_id is not a valid field in the given code. There is no field named camer_id in any of the data sources. The correct name is carrier_id.
B: ON Sprojection Camer=Source2 carrier_id is not valid because Sprojection and Source2 are not valid data sources in the given code. There is no CDS view or database table named Sprojection or Source2.
The correct names are Sprojection and Z_Source2. Moreover, the field Camer is not a valid field in the given code. There is no field named Camer in any of the data sources. The correct name is carrier_id. Furthermore, the ON condition is missing the dot (.) operator between the data source name and the field name, which is required to access the fields of the data source1.
C: ON Sprojection. Carrier Source2.carrier is not valid because Carrier and carrier are not valid fields in the given code. There is no field named Carrier or carrier in any of the data sources. The correct name is carrier_id. Moreover, the ON condition is missing the dot (.) operator between the data source name and the field name, which is required to access the fields of the data source1.
References: 1: ON Condition - ABAP Keyword Documentation