Mutations in the genetic code can occur when . A. the DNA is carried from the nucleus to the ribosome
B. DNA duplicates and an amino acid is changed
C. amino acids are transported from the cytoplasm to ribosomes
D. the cell divides into daughter cells

Mutations can only occur (from the options given) when DNA duplicates so, option would be the right answer :D

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.