Udp provides unreliable data transfer and therefore

a) should never be used
b) provides data security
c) provides congestion control
d) could be a good choice for loss-tolerant video and audio streams

The answer is d.

Explanation:

UDP is a transport protocol (Layer 4 of the OSI model) that has no mechanism to provide a reliable transport between the source process and the destination one, as TCP does.

Anyway, due to this feature, is specially suitable for real-time applications , like video or audio, provided that the user can accept some loss in the stream.

Several real-time protocols, like RTP for instance (used for videoconferencing)  use UDP as transport protocol.