Which country is constructing the Five hundred metre Aperture Spherical Telescope (FAST), known as the world largest single aperture radio telescope?

Introduction / Context:
Radio telescopes are powerful instruments used by astronomers to observe distant cosmic objects by detecting radio waves. The Five hundred metre Aperture Spherical Telescope, commonly called FAST, is designed to be the world largest single aperture radio telescope, significantly improving sensitivity for deep space observations. This question asks which country is responsible for building this giant scientific facility.

Given Data / Assumptions:
- The telescope is called FAST, with a diameter of about five hundred metres.
- It is described as the world largest single aperture radio telescope.
- The options are Japan, China, United States of America, and Russia.
- We assume some familiarity with recent developments in global astronomy infrastructure.

Concept / Approach:
FAST is located in a natural karst depression in Guizhou province and has been planned and built by China. It is often compared with the earlier Arecibo radio telescope in Puerto Rico, which had a smaller diameter. Remembering that China has invested in this massive radio astronomy project enables us to identify China as the correct answer among the given options.

Step-by-Step Solution:
Step 1: Recall the full name Five hundred metre Aperture Spherical Telescope and its abbreviation FAST. Step 2: Remember that FAST is a flagship science project of China and is located in Guizhou province. Step 3: Recognise that the earlier famous single dish radio telescope, Arecibo, was in United States territory but is not FAST. Step 4: Review the options and connect the project details with China space and science expansion efforts. Step 5: Select China as the country building this large radio telescope.

Verification / Alternative Check:
Reports in science news and general current affairs describe FAST as a Chinese project, sometimes calling it the Chinese super eye in the sky. Photographs and documentaries place the telescope in China karst landscape. Japan, the United States, and Russia all have important observatories, but the specific five hundred metre spherical telescope project is associated with China alone. This confirms that the correct option is China.

Why Other Options Are Wrong:
Japan: Japan has advanced technology and observatories but is not the country building FAST.
United States of America: Operated the Arecibo telescope in Puerto Rico, which was smaller than FAST and is a different project.
Russia: Has its own science facilities but is not linked to construction of the FAST telescope described here.

Common Pitfalls:
A common mistake is to confuse FAST with older large telescopes like Arecibo and wrongly choose the United States. Others may assume such a massive project must be in a long established space power and overlook China recent rapid growth in science infrastructure. Remembering the name association between FAST and China helps avoid such confusion.

Final Answer:
The Five hundred metre Aperture Spherical Telescope (FAST) is being constructed by China.