Rigorous study habits are important for developing intelligence, but it is a healthy and active physical regime also stimulates the brain.
a) intelligence, but a healthy and active physical regime it is that
b) intelligence, but then also a healthy and active physical regime
c) intelligence but it was a healthy and active physical regime
d) intelligence, but a healthy and active regime
e) no improvement or correction is required

D) intelligence, but a healthy and active regime.

Explanation: a coordinating conjunction is a conjunction placed between words, phrases, clauses, or sentences of equal rank (but, and, or). When we use a coordinating conjunction, we should put a comma before it. From the given options, the one that corrects the given sentence is the corresponding to option D, because it mantains the comma before "but" and it clarifies the sentence: "Rigorous study habits are important for developing intelligence, but a healthy and active regime also stimulates the brain."

faithful servants eumaeus and philaetius:

his ragged vest then drawn aside disclosed the sign conspicuous, and the scar exposed: eager they view'd, with joy they stood amazed with tearful eyes o'er all their master gazed:

these servants know ulysses by the scar he got when he was a child - so when he showed them the mark, they immediately knew this is truly their master and they hugged him, finally starting to believe his words.

you can use this site to summarize your ideas, exotic animals do not make good pets.