Answer:
"ser" and "estar", these two verbs differ on the condition of permanency of that what is being explained in the sentence.
It is better to use "ser" when you are expressing something that will be permanent, or most likely will be permanent.
it is better to use "estar" to express something that is likely to end in a short or medium term.
sometimes the verbs are interchangeable, in such cases is not needed to explain the length of the state expressed by the sentence.
The third sentence in the questions uses the literal translation from the English present continuous time to the Spanish "présente continuo"
