Explanation/Reference:
B: Normally, IS-IS metrics can have values up to 63. The total cost to a destination is the sum of the metrics on all outgoing interfaces along a particular path from the source to the destination. By default, the total path metric is limited to 1023. This metric value is insufficient for large networks and provides too little granularity for traffic engineering, especially with high-bandwidth links. A wider range of metrics is also required if route leaking is used.
C: By default, IS-IS protocol leaks routing information from a Level 1 area to a Level 2 area. However, to leak routing information from a Level 2 area to a Level 1 area, an export policy must be explicitly configured.
References: https://www.juniper.net/techpubs/en_US/junos16.1/topics/example/example-configuring-is-is- route-leaking-L2-to-L1.html
http://www.juniper.net/documentation/en_US/junos14.1/topics/topic-map/isis-wide-metrics.html