You are given a question or fill-in-the-blank question, two answer options (Option1 and Option2) and an Explanation. Your task is to find the correct answer (return the string of the correct option, not option1/2) for the given question from the given options and using explanation.

Q: Question: The the planets are colder than sun because they are 
 Option1: less massive 
 Option2: more massive 
 Explanation: An object with more mass has greater thermal energy than an object with less mass because it has more atoms.

A: less massive
****
Q: Question: If we find something with a low pH value that is likely to be 
 Option1: acidic 
 Option2: basic 
 Explanation: The higher the pH value is, the stronger the base.

A: acidic
****
Q: Question: Gerald laid down many rock layers. The layers on the top level were likely laid 
 Option1: first 
 Option2: last 
 Explanation: Lower rock layers were laid down earlier, so they are assumed to contain older fossils.

A:
last
****