There are 64 codons and 20 amino acids. which of the following is not true?
a. several different codons can specify the same amino acid.
c. all amino acids are linked to a codon.
d. each amino acid is specified by only one codon.

Well actually if you think about it some amino acids have no link to codon so my answer would be D 

It should be cryosphere and hydrosphere

The answer is atmosphere. there are four spheres of the earth: 1. geosphere (from greek word 'geo' = ground), 2. hydrosphere (from greek word 'hydro' = water), 3. biosphere (from greek word 'bio' = life), and 4. atmosphere (from greek word 'atmo' = air). a magnetosphere is a region of space around astronomical objects controlled by the magnetic field of that object. through the process of elimination, since lightning is present in the air, it can be found in the atmosphere.