Answer:

To understand why option A is the correct answer, let's first understand what a linked list is and how it works.

A linked list is a linear data structure consisting of nodes, where each node contains a value and a reference (or link) to the next node in the list. The first node is called the head, and the last node is called the tail. The tail node's reference points to null, indicating the end of the list.

When inserting a new node at the end of a linked list, the following steps are typically performed:

1. Traverse the list: Starting from the head, we need to traverse the entire list until we reach the tail node. This involves following each node's reference until we find the node that has a null reference, indicating the end of the list.

2. Create the new node: Once we reach the tail node, we can create a new node with the desired value.

3. Update the references: Set the reference of the tail node to the newly created node, making it the new tail. Then, set the new node's reference to null, indicating the end of the list.

Now, let's examine each option to determine which one is true:

a) It requires traversing the entire list: This statement is true because to insert a new node at the end of a linked list, we need to traverse the list from the head to the tail to find the last node.

b) It can be done in constant time: This statement is false because inserting a new node at the end of a linked list requires traversing the entire list, which takes linear time proportional to the number of nodes in the list.

c) It requires shifting all the elements: This statement is false because when inserting a new node at the end of a linked list, we only need to update the reference of the current tail node and create a new node. We do not need to shift any existing elements.

d) It is not possible in a linked list: This statement is false because inserting a new node at the end of a linked list is a common operation and can be easily performed by following the steps mentioned earlier.

Therefore, the correct answer is option A: It requires traversing the entire list.