Four of the following five words are units of length and so form a group. Choose the one word that does not belong to this group.

Introduction / Context:
This is a simple classification question dealing with measurement units. You are asked to identify which word among the given options does not represent the same kind of physical quantity as the others. Such questions test your basic knowledge of everyday and scientific units.

Given Data / Assumptions:

• The words given are Metre, Furlong, Yard, Mile and Acre.
• All of them are commonly used in measurement contexts.
• Metre is the SI unit of length.
• Furlong, yard and mile are traditional units of distance or length.
• Acre is a commonly used unit in land measurement.

Concept / Approach:
The core idea is to classify each word according to what it measures: length, area, volume or something else. If four items measure the same quantity and one measures a different quantity, then that one is the odd one out. Here the majority of terms are units of length or distance, and we need to check whether Acre follows the same category or not.

Step-by-Step Solution:
Step 1: Metre is a standard unit of length used in the metric system. It measures one dimensional distance.Step 2: Yard is an imperial or customary unit of length, often used in countries that use the imperial system.Step 3: Mile is another traditional unit of length, used especially for longer distances such as road travel.Step 4: Furlong is an older unit of length, traditionally used in agriculture and horse racing, equivalent to one eighth of a mile.Step 5: All four of these units (Metre, Yard, Mile, Furlong) measure one dimensional distance or length.Step 6: Acre, by contrast, is a unit of area, not length. It is used to measure the size of land, and represents a two dimensional measurement (length multiplied by width).Step 7: Therefore, four options are units of length, and Acre is a unit of area.Step 8: The word that does not belong to the group of length units is Acre.

Verification / Alternative check:
To confirm, imagine what question each unit answers. Metre answers \"how long\" is something. Yard and Mile also answer \"how long\" or \"how far\". Furlong answers \"what distance\" for old racing tracks. Acre, however, answers \"how large is this piece of land\" in terms of surface area. You cannot use Acre to measure the length of a road or the height of a building, which again shows the category difference.

Why Other Options Are Wrong:
Metre, Furlong, Yard and Mile are all clearly units of length. Their numerical values or systems (metric vs imperial) may differ, but they belong to the same category of one dimensional measurement. Because they share the same type of quantity, they form the majority group and cannot be the odd one out. Only Acre measures a two dimensional quantity.

Common Pitfalls:
Sometimes candidates remember that Acre is strongly associated with land and fields but forget precisely that it measures area. Others may confuse Yard with a backyard or Mile with a milestone and get distracted by everyday meanings. To answer correctly, focus on the technical role as a unit and ask, \"Is this used to measure distance or something else?\"

Final Answer:
The word which does not belong with the others is Acre.