CATGGATCCA for future reference this is considered biology, you may get a quicker response if you categorize it as such :)
Answer:
not sure if this is the right way to answer this question but PbS is Phosphate-buffered saline (i think)
Explanation:

If the half-life of a sample of a radioactive substance is 30 seconds, how much would be left after 60 seconds? <span>
A. one-fourth</span>
They do not show the same season. one is faced a different part of the sun