This question involves identifying the major product U in a multi-step organic reaction sequence. Since the specific reaction images are not fully interpretable in text, I will explain the general approach to solving such problems, focusing on common reaction mechanisms and logical deduction.

Step-by-Step Approach:

Step 1: Analyze the Starting Material
The reaction likely begins with a compound containing a functional group that undergoes a specific transformation. Common starting points include alkenes, alcohols, or carbonyl compounds.

Step 2: Identify Each Reaction Step
Each arrow represents a reaction. You need to recognize the reagents and conditions to predict the product at each stage. For example: - Reagents like ${\mathrm{BH}}_3·{\mathrm{THF}}_{}$ followed by $H_2{O}_2,{\mathrm{OH}}^{-}$ indicate hydroboration-oxidation, which adds water anti-Markovnikov to an alkene. - Reagents like $\mathrm{PCC}$ or ${\mathrm{CrO}}_3$ oxidize alcohols to aldehydes or ketones. - Grignard reagents ($\mathrm{RMgX}$) add to carbonyls to form alcohols.

Step 3: Track Structural Changes
After each reaction, note how the carbon skeleton and functional groups change. Consider stereochemistry if relevant (e.g., syn/anti addition).

Step 4: Predict the Final Product U
Combine all steps to deduce the structure of U. Ensure it matches one of the given options in terms of functional groups and carbon chain.

Step 5: Verify with Options
Compare your predicted structure with the provided images. Look for key features like rings, functional groups (e.g., OH, C=O), or specific substituents.

Related Topics & Formulae:

Hydroboration-Oxidation: Converts alkenes to alcohols with anti-Markovnikov orientation and syn addition.
$R-\mathrm{CH}=\mathrm{CH}2\stackrel{{\mathrm{BH}}_3,H_2{O}_2/{\mathrm{OH}}^{-}}{\to }R-\mathrm{CH}2-\mathrm{CH}2\mathrm{OH}$

Oxidation of Alcohols: Primary alcohols to aldehydes (with PCC) or carboxylic acids (with stronger oxidizers); secondary alcohols to ketones.
$R-\mathrm{CH}2\mathrm{OH}\stackrel{\mathrm{PCC}}{\to }R-\mathrm{CHO}$

Grignard Addition: Reacts with carbonyls to form new C-C bonds, yielding alcohols after hydrolysis.
$R-\mathrm{CHO}+R^{\prime }\mathrm{MgX}\to R-\mathrm{CH}\left(R^{\prime }\right)-\mathrm{OMgX}\stackrel{H_{2}O}{\to }R-\mathrm{CH}\left(R^{\prime }\right)-\mathrm{OH}$

Without the exact structures, this general method should guide you. Practice with known reactions to improve prediction skills.