In the following English idiom question, the phrase "Rule to roost" is given. Out of the four alternatives, select the option that best expresses the intended idiomatic meaning, keeping in mind the common expression "rule the roost" used in English.

Introduction / Context:
The phrase printed in the question as "Rule to roost" is clearly a variant of the well known English idiom "rule the roost". This expression is used to describe someone who dominates a place, group, or situation, making most of the decisions. Idiomatic questions like this check whether candidates can recognise the correct underlying expression and recall its standard meaning related to power and control, rather than interpreting individual words literally.

Given Data / Assumptions:
- The phrase in the question corresponds to the idiom "rule the roost".
- The options are: to repent, to dominate, to understand, and to apologize.
- Only one option correctly reflects the idiomatic meaning of having authority or control.
- We assume contexts such as family, workplace, or social groups where one person clearly holds the main power.

Concept / Approach:
In its original imagery, a "roost" is a perch where birds, especially chickens, rest. The bird that "rules the roost" dominates the others. In human contexts, the idiom describes a person who is in charge, exercises control, or dominates decision making. Therefore, we must select an option that refers to dominating or having authority, not to repentance, comprehension, or apology.

Step-by-Step Solution:
Step 1: Recall sentences such as "In that household, the grandmother rules the roost" or "The manager rules the roost in the office". Step 2: Interpret these examples. In both cases, the person mentioned has the final say and exercises strong authority over others. Step 3: Examine option B, "To dominate". This directly expresses the idea of having control or power over others and fits the idiom perfectly. Step 4: Evaluate option A, "To repent". This refers to feeling sorry for wrong actions and is about personal regret, not authority. Step 5: Evaluate option C, "To understand". This relates to comprehension and has nothing to do with power or leadership. Step 6: Evaluate option D, "To apologize". This involves expressing regret to someone, which is again unrelated to dominating or ruling. Step 7: Hence, option B is the correct answer because it alone captures the sense of domination or control.

Verification / Alternative check:
Standard definitions describe "rule the roost" as "to be the person in a group who makes all the decisions" or "to be in complete control". If we substitute "dominate" into example sentences, they remain meaningful: "In that household, the grandmother dominates" matches the sense of ruling the roost. The other options, when inserted, fail to preserve the meaning and often produce sentences that are logically odd or completely different in tone.

Why Other Options Are Wrong:
- "To repent" concerns moral regret and has nothing to do with social power or authority.
- "To understand" is about mental comprehension and cannot describe someone's ruling position.
- "To apologize" is an act of admitting fault, which is almost the opposite of asserting dominance.

Common Pitfalls:
Candidates may be confused by the slight misprint "rule to roost" and hesitate, thinking that it might have a different meaning. However, exam questions often assume that test takers will recognise the familiar idiom "rule the roost". Other students might try to interpret "roost" literally and imagine birds repenting or understanding, which leads to incorrect choices. To avoid such errors, it is important to recognise common idioms quickly and recall their standard use in describing power relations.

Final Answer:
The idiom represented by "Rule to roost" (that is, "rule the roost") means to dominate or to be in complete control.