Additions or deletions of bases in the nucleotide sequence of a structural gene most often result in
(a) an altered sequence of amino acids in the protein that the gene encodes
(b) insertion of a new intron into the coding sequence of the gene
(c) decreased histone binding
(d) decreased excision repair
(e) increased levels of mrna production

The correct answer is A. bicycling

Explanation:

The ability of lungs and heart to supply sufficient oxygen for the working muscle during an extended period of aerobic activity is called cardiorespiratory fitness.

Aerobic exercise is the best exercise that can help in improving cardiorespiratory fitness. Aerobic exercise helps in increasing cardiorespiratory fitness because during aerobic exercise the respiratory rate and heart rate enhances.  

Bicycling is one of the best aerobic exercises by which we can improve our cardiorespiratory fitness. Therefore the correct answer is A.