In this question based on the TRAPPIST 1 passage, you must recall how many planets in our own solar system are stated to have liquid water, according to the information provided in the text.

Introduction / Context:
The passage that discusses the TRAPPIST 1 system uses our own solar system as a point of comparison when talking about liquid water. It stresses how special the seven Earth size exoplanets are because they may have liquid water, and then contrasts this with the situation in our solar system. The text explicitly states how many planets in our system currently have liquid water. This question tests your ability to recall that specific factual detail rather than interpret or infer from general science knowledge.

Given Data / Assumptions:

• The passage notes that the seven TRAPPIST 1 planets could possibly have liquid water.
• It then contrasts this with the situation in the solar system we live in.
• The passage clearly states that only Earth has liquid water in the solar system.
• The options provide different possible counts of planets with liquid water.
• We assume the reader understands that the question refers to the explicit wording of the passage.

Concept / Approach:
In reading comprehension, the most reliable method for fact based questions is to locate the exact sentence that mentions the required information. Here, the important line is the one that declares that only Earth has liquid water in the solar system. The phrase only Earth implies a count of one. Therefore, regardless of any scientific discussion about possible subsurface oceans on other moons or planets, the correct answer must reflect the passage wording. Focus on the expression only Earth and convert it into the numerical value that best matches among the options, which is one.

Step-by-Step Solution:

Verification / Alternative check:
To verify, examine each option and consider whether it fits the wording only Earth. If there were two, three, or more planets with liquid water, the passage would not use only to single out Earth. Options claiming two, three, four, or five planets contradict the explicit statement. Furthermore, the focus of the passage is to show why the TRAPPIST discovery is remarkable when compared with the situation in our solar system, and emphasising that only one planet currently has liquid water strengthens that contrast. Thus, the logical and textual evidence supports choosing One as the correct answer.

Why Other Options Are Wrong:
Two, three, four, and five are all incorrect because they directly conflict with the phrase only Earth used in the passage. None of these numbers can be reconciled with the wording that singles out only one planet. While scientific discussions may consider water in different states on moons or dwarf planets, this is beyond the scope of the passage. The exam expects you to answer according to the text provided, not external sources. Therefore, any number greater than one must be rejected as inconsistent with the passage.

Common Pitfalls:
A common pitfall is to rely on general astronomy knowledge about icy moons or suspected subsurface oceans and to reason that more than one body in the solar system has water. However, the passage is about liquid water and uses a simple comparison, highlighting Earth as the only planet with liquid water. Another mistake is careless reading, where students recall that water was mentioned but forget the precise qualifier only Earth. To avoid such errors, always underline key quantifiers like only, all, or several when reading a passage, as these words often become the basis of exam questions.

Final Answer:
According to the passage, there is one planet in our solar system that has liquid water, namely Earth.