Correct answer is AD https://www.juniper.net/documentation/us/en/software/junos/cos-security-devices/topics/concept/cos-transmission-scheduling-security-overview.html

A / D seem to be correct

AD is correct.

By default, each queue can exceed the assigned bandwidth if additional bandwidth is available from other queues. When a forwarding class does not fully use the allocated transmission bandwidth, the remaining bandwidth can be used by other forwarding classes if they receive a larger amount of offered load than the bandwidth allocated. A queue receiving traffic within its bandwidth configuration is considered to have positive bandwidth credit, and a queue receiving traffic in excess of its bandwidth allocation is considered to have negative bandwidth credit. https://www.juniper.net/documentation/us/en/software/junos/cos-security-devices/topics/concept/cos-transmission-scheduling-security-overview.html

a AND d IS CORRECT

De forma predeterminada, cada cola puede exceder el ancho de banda asignado si hay ancho de banda adicional disponible en otras colas. Cuando una clase de reenvío no utiliza completamente el ancho de banda de transmisión asignado, el ancho de banda restante puede ser utilizado por otras clases de reenvío si reciben una cantidad mayor de carga ofrecida que el ancho de banda asignado. Se considera que una cola que recibe tráfico dentro de su configuración de ancho de banda tiene un crédito de ancho de banda positivo, y una cola que recibe tráfico que excede su asignación de ancho de banda tiene un crédito de ancho de banda negativo.

In this scenario, the two default actions taken by a Junos device are: B. The excess traffic will be discarded. D. The excess traffic will use bandwidth available from other queues.

If a queue exceeds its allocated bandwidth, it is considered to have negative bandwidth credit and its excess traffic will be discarded by default.