Using the chart, which of the following point mutations will cause the most harmful effect on an individual?

a. the sequence reads auu; a change in the second base from u to c
b. the sequence reads cga; a change in the first base from c to a
c. the sequence reads ugu; a change in the third base from u to a
d. the sequence reads uua; a change in the first base from u to c and a change in the third base from a to g