The reaction which forms a pair of diastereomers


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> The reactions among the following which results in the formation of a pair of diastereomers are:
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> [![enter image description here](https://i.stack.imgur.com/OwiYS.jpg)](https://i.stack.imgur.com/OwiYS.jpg)
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I am aware of the fact that $\ce{HBr}$ gives anti addition product and $\ce{BH3}$ forms syn addition product. In part (a) since the back side is less sterically hindered ( due to presence of only $\ce{H}$ ) $\ce{BR-}$ preferentially attacks from the back side.Similar is the case with (b).c) proceeds with a free radical mechanism.d) however occurs via anti-markinicoff addition so that $\ce{OH}$ adds to the primary carbon.Since there are two possible ways in which the $\ce{OH}$ group may add( either from the back side or the front side)my idea is that it may result in a pair of diastereomers. However I am not quite sure about it. Thanks.


