Which of the following is$/$are correct?

Question $3$Select one or more:

a$.$

All NoSQL databases are scalable.

b$.$

Scale up means to add more nodes to a system, e$.$g$.$ adding more web servers.

c$.$

Relational databases often cannot scale beyond certain point under ACID constraints.

d$.$

NoSQL databases often consider to scale out by using commodity hardware and free software.