A proxy server can filter internet access by controlling which websites or services users can reach. It enforces content policies and can provide caching and monitoring.
A). A router directs traffic but doesn't filter internet sites by itself.
B). A cloud gateway could also filter, but the most direct answer is proxy.
D). An IDS detects suspicious activity but doesn't filter browsing access.
References (CompTIA Network+ N10-009):
Domain: Network Security - Proxy servers, filtering, access control.