The answer is B. estudiante.
The article preceding it, 'las', is the plural feminine article. 'estudiante' in the sentence is singular only, but it is gender neutral. 'son' is the third person plural conjugation of the verb 'ser'. 'inteligentes' is an adjective that would refer to plural subjects. To fix the sentence, change 'estudiante' to 'estudiantes'.
<h3>Complete these sentences with the subjunctive or indicative of the verbs in brackets, depending on context. </h3>
Tenemos que conservar agua aunque haya¹ suficiente agua ahora. Cuando desaparecen² los bosques, se pierden muchas especies. La gente se preocupará por el calentamiento de la tierra cuando sea³ demasiado tarde. Los carros seguirán contaminando hasta que nosotros encontremos⁴ mejores combustibles alternativos Las especies en peligro de extinción comenzarán a recuperarse tan pronto como nosotros hagamos⁵ algo para protegerlas. Los recursos naturales se agotarán a menos que todas las personas del planeta los conservemos⁶.
Translation: <em>We have to conserve water even though there is enough water now. When forests disappear, many species are lost. People will worry about the warming of the earth when it is too late. The cars will continue to pollute until we find better alternative fuels. Endangered species will begin to recover as soon as we do something to protect them. Natural resources will be exhausted unless all the people of the planet conserve them.</em>
I wouldn’t be able to do it !
No podría hacerlo !
Are you asking for a verb or is there some sort of word bank???