Answer:
The correct answer is A. Nadábamos
Explanation:
We used to swim, corresponds to the imperfect preterite, translated as "soliamos nadar"/"nadabamos"
Said tense refers to past situations, without relevant time limits.
I assume you mean the verb conjugation of the present perfect? It's used to talk about things that started in the past, but are still going on right now (in the present) or something that happened recently.
To form it use the past participle of haber + the past participle of another word. For example:
He visto las montañas de Perú
(I have seen the mountains of Peru)
Hemos vuelto para comprar la leche
(We have returned to buy milk)
Habéis cantado muy bien
(You have/You've sung very well)
If you need more info, here is a good place: http://www.spanishdict.com/guide/spanish-present-perfect-indicative
“Se compran zapatos” this sentence makes sense bc it’s a neutral. Meaning that is not directly to someone or something
Answer:
The half life of an isotope is the time that an element take to reduce the half of the mass.
Explanation:
So for example,in the case of carbon 14, one gram takes 5730 years to reduce to 0.5 g, and then, it takes another 5730 years to be reduced to 0.250 g and so and so.
So depending the mass of the sample that you have, for example, a bone that weights 15 g, it will take 5730 years to have a mass of 7.5 g, and then 11, 460 years to have a mass of 3.75 g, and then 17,190 years to have a mass of 1.875 g, and so, and so.
Hope this info is useful.
