Explanation/Reference:
B: Query Roots
For a particular CriteriaQueryobject, the root entity of the query, from which all navigation originates, is called the query root. It is similar to the FROM clause in a JPQL query.
D: Criteria queries may have more than one query root. This usually occurs when the query navigates from several entities.
The following code has two Root instances:
CriteriaQuery<Pet> cq = cb.createQuery(Pet.class);
Root<Pet> pet1 = cq.from(Pet.class);
Root<Pet> pet2 = cq.from(Pet.class);
Reference: The Java EE 6 Tutorial, Chapter 23 Using the Criteria API to Create Queries