Polling behaviour when a consumer assigned with multiple topics-partition

Hi,

I want to know the polling behaviour when a consumer is assigned with
multiple topic-partitions.

1. In a single poll will it get messages from multiple topic-partitions. Or
in one poll only one topic-partition's messages will come?

2. How does it choose topic-partitions for next polling? Any default
class/strategy assigned for this, that we can reconfigure?

Thanks
Upendra