Given edge lengths and face angles, predict the shape of
each of the following crystals.
$$
\begin{aligned} \text { a. } & a=3 \mathrm{nm}, b=3 \mathrm{nm}, c=3 \mathrm{nm} ; \alpha=90^{\circ}, \beta^{\circ}=90 \\ & \gamma=90^{\circ} \\ \text { b. } & a =4 \mathrm{nm}, b=3 \mathrm{nm}, c=5 \mathrm{nm} ; \alpha=90^{\circ}, \beta^{\circ}=100 \\ & \gamma=90^{\circ} \\ \text { c. } & a=3 \mathrm{nm}, b=3 \mathrm{nm}, c=5 \mathrm{nm} ; \alpha=90^{\circ}, \beta^{\circ}=90 \\ & \gamma=90^{\circ} \\ \text { d. } a &=3 \mathrm{nm}, b=3 \mathrm{nm}, c=5 \mathrm{nm} ; \alpha=90^{\circ}, \beta^{\circ}=90 \\ & \gamma=120^{\circ} \end{aligned}
$$