In English vocabulary and one word substitution, which word correctly means that something can be believed because it appears reasonable and trustworthy. Choose the most appropriate word for the definition "that which can be believed".

Introduction / Context:
This question tests fine distinctions between similar looking English words. In one word substitution and vocabulary items, "Credible", "Creditable", and "Gullible" often confuse learners. The given definition is "that which can be believed". To answer correctly, we must know the precise meaning of each option.

Given Data / Assumptions:
- The required word must mean capable of being believed.
- It refers to statements, information, reports, or explanations that appear reliable.
- The word is used to describe the quality of believability, not the quality of being praiseworthy or naive.

Concept / Approach:
"Credible" means believable or convincing. If a story is "credible", people feel that it could be true. "Creditable" means deserving praise or approval. "Gullible" describes a person who is too ready to believe what others say. "Miraculous" and "Verifiable" have different nuances. So the task is to choose the word that best matches "that which can be believed".

Step-by-Step Solution:
Step 1: Focus on the core idea: something can be believed because it sounds reasonable or convincing. Step 2: Recall that "Credible" is used in phrases like "a credible explanation", "a credible witness", and "a credible threat". Step 3: Compare this with "Creditable", which appears in sentences like "She made a creditable effort", meaning an effort worthy of praise. Step 4: Note that "Gullible" is used for people who believe things too easily, not for statements or reports. Step 5: "Miraculous" suggests something amazing and almost impossible, like a miracle, which is the opposite of ordinary believability. Step 6: "Verifiable" means that something can be checked or tested, but it does not automatically mean people already find it believable. Step 7: Therefore, "Credible" is the only option that matches "that which can be believed".

Verification / Alternative check:
Dictionaries define "Credible" as "able to be believed" or "convincing". Many exam guides emphasise the difference between "Credible" (believable) and "Creditable" (praiseworthy). Example sentences and practice questions repeatedly reinforce this distinction. Cross checking with such sources confirms that "Credible" is the appropriate answer.

Why Other Options Are Wrong:
"Miraculous" describes something like a miracle and does not relate to simple believability. "Creditable" is about deserving credit or praise, not about being believable. "Gullible" is a description of a person who is easily fooled, not of information. "Verifiable" indicates that something can be checked, but a statement might be verifiable yet still not credible until the verification is done.

Common Pitfalls:
The most common mistake is picking "Creditable" because it looks similar to "Credible" and shares the root "cred", meaning belief. However, in modern English they have clearly separated meanings. Another confusion arises between "Credible" and "Incredible". Remember that "Incredible" often means hard to believe, while "Credible" means easy to believe. Keeping these pairs in mind will help avoid errors in exams.

Final Answer:
The correct one word substitution for "that which can be believed" is Credible.