Cyanohydrin of which of the following forms lactic acid?

Which is the most suitable reagent for the following conversion?
$CH_3-CH=CH-CH_2-CO-CH_3 \rightarrow CH_3-CH=CH-CH_2-COOH$

Reaction of a carbonyl compound with one of the following reagents involves nucleophilic addition followed by elimination of water. The reagent is

Identify the group $R$ in the following reaction:
$CH_3CH_2CHO \xrightarrow[2. H_3O^+]{1. RMgBr} CH_3CH_2CH(OH)CH_2CH_3$
$R$ is:

Find the major product of the following reaction: $C_6H_5CHO + CH_3CHO \xrightarrow{Ca(OH)_2, \Delta} ?$

What are $A, B, C$ and $D$ in the following cross-aldol condensation reaction?
$\text{Propanal} + \text{Ethanal} \xrightarrow[ii) \ \Delta]{i) \ NaOH} A + B + C + D$
(The products are the four possible $\alpha,\beta$-unsaturated aldehydes formed by self and cross-aldol condensation followed by dehydration.)