Important for :
The demand for many industrial products for which a price increase or decrease will not significantly affect the demand is :
» Explain it
Demand whose percentage change is less than a percentage change in price. For example, if the price of a commodity rises twenty-five percent and demand decreases by only two percent, demand is said to be inelastic.

In simpler words, A situation in which the demand for a product does not increase or decrease correspondingly with a fall or rise in its price.

Option 'B' hence is the correct answer. 
When the requirements associated with a new-task purchase are changed the second or third time, this is called a:
» Explain it
Modified Rebuy is a buying situation in which an individual or organization purchase goods that have been purchased previously but changes either the supplier or some other elements of the previous order. In this the buyer wants to modify product specifications, terms, prices, suppliers.

Option 'A; hence is the most obvious choice here.
The group of people within an organisation who are involved in making organisational purchase decisions is referred to as:
» Explain it
A buying center brings together "all those members of an organization who become involved in the buying process for a particular product or service". Buying centers are also sometimes known as 'decision-making units'.

Option 'E' hence is the correct answer.
For routinely purchased items, buyers are frequently the:
» Explain it
Routine decision-making involves purchases that require very little thought after the original decision has been made. Therefore, in such scenario buyers are frequently the deciders.

Option 'C' hence is the correct answer.
After deciding to order replacement parts for aging machinery, the buyer for a construction company examines catalogues and trade publications. The buyer is probably at which stage of the organisational buying decision process?
» Explain it
Stages of the Business Buying Decision Process
Step 1: Recognize the Problem.
Machine malfunction, firm introduces or modifies a product, etc.
Step 2: Develop product specifications to solve the problem.
Buying center participants assess problem and need to determine what is necessary to resolve/satisfy it.
Step 3: Search for and evaluate possible products and suppliers.
Look in company files and trade directories, contact suppliers for information, solicit proposals from known vendors, examine websites, catalogs, and trade publications conduct a value analysis - an evaluation of each component of a potential purchase; examine quality, design, materials, item reduction/deletion to save costs, etc. conduct vendor analysis - a formal and systematic evaluation of current and potential vendors; focuses on price, quality, delivery service, availability and overall reliability.

Step 4: Select product and supplier and order product.
An organization can decide to use several suppliers, called multiple sourcing. Multiple sourcing reduces the possibility of a shortage by strike or bankruptcy. An organization can decide to use one supplier, called sole sourcing. 
Step 5: Evaluate Product and supplier performance
Understanding the stages of business buying and the nature of customers' buying behavior is important to a marketing firm if it is to market its product properly. In order to entice and persuade a consumer to buy a product, marketers try to determine the behavioral process of how a given product is purchased.

Option 'C' hence is the correct answer here.