The rare earth elements include
a. the lanthanide series and the alkali metals.
b. the alkali metals and the transition metals.
c. the actinide series and the alkaline earth metals.
d. the lanthanide series and the actinide series.

I know that the  rare earth elements (rare earths) - a group of 17 elements consisting of lanthanum, scandium, yttrium and the lanthanides. All these elements - metals silver-white color, while all have similar chemical properties (most common in oxidation state +3). The name "rare earth" is defined in connection with the fact that they are, first, relatively rare in the crust (the content of (1.6-1.7) x 10-2% by weight) and, secondly, to form a refractory substantially water-insoluble oxides (oxides of these at the beginning of the XIX century and formerly known as "lands"). 

That is why the correct answer is D)

Spherical shaped cell might increase the surface area and decrease the volume.