What makes the galápagos islands so special?

(1) the galápagos islands are a special place. (2) most famously, the islands had a major effect on the work of naturalist charles darwin. (3) his visit there in 1835 was important to his study of animal species. (4) today, the islands are the dream destination of many biologists and lovers of unique birds and reptiles.
(5) the galápagos islands are interesting in part because of their geography. (6) they are located about 600 miles off the coast of ecuador, in the pacific ocean. (7) there are no other islands nearby, so that makes them quite isolated. (8) the major islands are made up of a single volcano, though sometimes more than one. (9) volcanic activity continues there to this day. (10) these dramatic processes provide scientists with information about how the islands first came to be.
(11) the galápagos islands are of special interest to biologists because of their rare plant and animal life. (12) scientists believe the islands' location is a major reason why the islands are unique. (13) the galápagos islands are located right where three major ocean currents come together. (14) these currents are believed to have animals, such as seals and sea lions, to swim to the islands. (15) such animals would not normally be found so far from the mainland. (16) the currents also cause the water temperatures to vary. (17) this makes it possible for different sea animals to live there than other places. (18) the islands' location and the ocean currents have allowed some very unusual creatures to develop. (19) among the most famous are the world's largest tortoises. (20) giant tortoises can be found on the islands called seychelles, in the indian ocean. (21) the tortoises on the galápagos can weigh up to 550 pounds and live for over 100 years!

(8) the major islands are made up of a single volcano, though sometimes more than one. (9) volcanic activity continues there to this day.

without changing the meaning or omitting important information, what is the best way to combine sentences 8 and 9?

a. the major islands are made up of one volcano or sometimes made up of more, and these volcanoes have activity sometimes today.

b. the volcanic activity continues there even to this day, and the major islands are made up of a volcano or two.

c. volcanic activity continues even to this day on islands with a volcano, and these islands may have more than one.

d. the major islands are made up of one or more volcanoes, and volcanic activity continues there today.