Meaning: 'By' means 'not later than' or 'before a certain time,' indicating that by the year 1425, Murad II had completed his actions.

Wrong options:

• Over: 'Over' typically indicates movement across a surface or a period of time, which does not fit the temporal context required here.
• Until: 'Until' suggests a continuation up to a certain point, which does not convey the completion of actions by a specific time.
• Through: 'Through' implies movement from one end to another, which does not align with the intended meaning of completing actions by a certain date.

Correct answer: over

Explanation: The preposition 'over' indicates control or dominance over a region, aligning with the context of Murad II's re-establishment of Ottoman rule over the Turkmen principalities.

Meaning: 'Over' in this context means 'in control of' or 'dominant in,' referring to the Ottoman authority established in the region.

Wrong options:

• toward: 'Toward' indicates direction rather than control, which does not fit the context of ruling over principalities.
• under: 'Under' suggests subordination or being beneath something, which does not accurately describe the nature of Ottoman rule.
• for: 'For' indicates purpose or benefit, which does not convey the idea of ruling or control in this context.
• onto: 'Onto' implies movement towards a surface, which is not relevant to the concept of ruling over a territory.

Correct answer: then

Explanation: The adverb 'then' indicates a sequence of events, fitting grammatically and contextually as it shows the chronological order of Murad II's actions after eliminating his rivals.

Meaning: 'Then' means 'at that time' or 'next,' indicating the subsequent action taken by Murad II after his previous accomplishments.

Wrong options:

• after: 'After' suggests a time following an event but does not fit as smoothly in the sequence of actions as 'then' does.
• so: 'So' indicates a consequence rather than a sequence, which does not align with the intended meaning of the timeline.
• before: 'Before' indicates a prior time, which contradicts the chronological flow of events presented in the text.
• too: 'Too' implies addition or excess, which does not fit the context of sequential actions.

Correct answer: At first

Explanation: The phrase 'At first' introduces the initial phase of events, fitting grammatically and contextually as it sets the stage for the subsequent description of the Ottoman armies' success.

Meaning: 'At first' means 'initially' or 'in the beginning,' indicating the starting point of the Ottoman military actions.

Wrong options:

• In beggining: 'In beggining' is grammatically incorrect; the correct phrase is 'In the beginning,' which is less formal than 'At first.'
• In the first place: This phrase is more commonly used to introduce a list or argument rather than to indicate the start of a sequence, making it less suitable here.
• At start: 'At start' is not a standard phrase in English; 'At first' is the correct and idiomatic expression.
• First of all: This phrase is typically used to introduce points in a list rather than to indicate the beginning of a sequence of events.

Correct answer: but

Explanation: The conjunction 'but' introduces a contrast, fitting grammatically and contextually as it highlights the shift from initial success to subsequent losses faced by the Ottomans.

Meaning: 'But' means 'however' or 'on the contrary,' indicating a change in circumstances from success to defeat.

Wrong options:

• however: While 'however' also indicates contrast, it is more formal and does not fit as smoothly in the sentence structure as 'but.'
• while: 'While' suggests simultaneous actions rather than contrast, which does not align with the intended meaning of the sentence.
• also: 'Also' indicates addition rather than contrast, making it unsuitable for the context of the sentence.
• allthough: 'Allthough' is a misspelling of 'although,' which introduces a subordinate clause rather than a direct contrast, making it grammatically incorrect in this context.