Answer
Grignard reagents add to aldehydes to give, after protonation, secondary alcohols.
The two alkyl groups of the secondary alcohol are the alkyl group from the Grignard reagent and the alkyl group that was bonded to the carbonyl group of the aldehyde.
Work Step by Step
There are two ways to synthesize 1-cyclohexylbut-3-en-1-ol using a Grignard reagent.
The first way is to use cyclohexanecarbaldehyde and allylmagnesium bromide as a Grignard reagent.
Another way is to use but-3-enal, and as a Grignard reagent, we can use cyclohexylmagnesium bromide.
In both ways, we get the same product, but a new C-C bond is formed at the two different sites indicated in the figures.
* Solvent is not indicated in the figures, but these reactions take place in ether or THF.