Answer:
D. New species of iguanas
Explanation:
A- doesn't make sense because nature changes every day.
B- More islands is possible but not likely considering your other options.
C- More tortoises is also possible but because I haven't read your text book or where your learned this information I can't be sure this is it.
D- Is the likeliest
I honestly think that a or d would be the best options. I would start with D and if that doesn't work try a.