The major product in the reaction is
`CH_(3)-underset(CH_(3))underset(|)CH-CH_(2)Br underset(CH_(3)OH)overset(CH_(3)O^(-))to`

Options

A. `CH_(3)-underset(OCH_(3))underset(|)CH-CH_(2)CH_(3)`
B. `CH_(3)-underset(CH_(3))underset(|)C=CH_(2)`
C. `CH_(3)-underset(CH_(3))underset(|)CHCH_(2)OCH_(3)`
D. `CH_(3)-underset(OCH_(3))underset(|)overset(CH_(3))overset(|)C-CH_(3)`

Explanation

To determine the major product of the reaction involving `CH₃-CH(CH₃)-CH₂Br` with `CH₃OH` and `CH₃O⁻`, we will analyze the reaction step by step.

### Step 1: Identify the Reactants
The reactants are:
- `CH₃-CH(CH₃)-CH₂Br` (which is a haloalkane)
- `CH₃OH` (methanol)
- `CH₃O⁻` (methoxide ion, which acts as a base)

### Step 2: Determine the Role of the Base
In this reaction, `CH₃O⁻` acts as a base. Bases can either participate in nucleophilic substitution reactions or elimination reactions. Given that we have a haloalkane and a strong base, we can expect an elimination reaction (E2 mechanism) to occur.

### Step 3: Identify the Elimination Mechanism
In an E2 elimination, the base abstracts a proton (H) from a β-carbon (the carbon adjacent to the carbon bearing the leaving group, Br in this case) while the leaving group (Br) departs simultaneously.

### Step 4: Identify the β-Hydrogens
The structure `CH₃-CH(CH₃)-CH₂Br` has the following β-hydrogens:
- The hydrogen on the `CH₂` group (the carbon attached to Br) is a β-hydrogen.
- The hydrogen on the `CH` group (the carbon attached to the first `CH₃`) is also a β-hydrogen.

### Step 5: Choose the β-Hydrogen to Abstract
The base `CH₃O⁻` will abstract one of the β-hydrogens. In this case, it will abstract the hydrogen from the `CH₂` group because this leads to the formation of a more stable alkene product.

### Step 6: Elimination of the Leaving Group
As the base abstracts the β-hydrogen, the Br atom leaves, resulting in the formation of a double bond between the two carbons involved in the elimination.

### Step 7: Draw the Major Product
After the elimination, the structure will look like this:
- The double bond will form between the `CH` and `CH₂` groups.
- The product will be `CH₃-CH=CH₂` (propene).

### Final Product
The major product of the reaction is:
`CH₃-CH=CH₂` (propene).