open cloze

Well, Sheppard Software seem to agree with me that "system" and "although" fit quite well!

There is a comma and an "is" missing from the question text.

Some whale species have a sophisticated social system. Their communication system may contain some of the elements of true language, although our knowledge of whale communications is not very advanced. Many other animals, including insects, have complex social systems, and many others, such as birds, have sophisticated communications. Whales also have very acute hearing, which gives them advanced echo-location capacities analogous to sonar - but so do bats. All this has led many (though far from all) zoologists to the conclusion that there is no convincing evidence for whale intelligence. A better understanding of whale communications and whale behaviour may solve this problem eventually.

http://www.sheppardsoftware.com/content/animals/groups/profile_long_whales.htm

Hi Contrex

Thank you very much for your invaluable guidance.

What is 'Sheppard Software'? Have we to buy it or can it be found in Google?

Many thanks.

Well if you are going to talk about them, you might as well look at one.
This is the type we have where I live. Orca aka Killer Whale (Killer does not = mean, they are friendly)

http://wdfw.wa.gov/science/articles/pcb/index.html

My goodness! Killer Whales are friendly. You'd better prove to me before I go near it.

I petted one but, I don't have "proof". I was in a boat and the whales were curious and came over. So, you shut the motor off because you don't want to hurt them.

The (Orca) Killer Whale
(Orcinus orca)

"The Killer whale is the largest member of the dolphin family. This distinctive jet-black, brilliant white and grey marked, huge dorsal finned male, makes this animal relatively easy to identify. The female and juvenile, at a distance however, can be confused with Risso's dolphin, the False Killer whale and even Dall's Porpoise. The Orca can grow to a length of 7m (23ft) and weigh 4-5,000 kg in the male and 6.6m (21ft) 2.5-3,000 kg in the female.
Despite it's name, the Killer whale has never hurt a person in the wild. It is inquisitive and approachable and aggression within a pod is rare. The pod is a close-knit family group and is stable from one generation to the next. It's members usually stay together for life. When two or more pods come together temporarily the group is called a "superpod" and may number more than 150 whales. Usually larger groups split up into two or more smaller ones as the population grows. These groups of closely related pods (clans) often develop their own dialects."

http://images.google.com/imgres?imgurl=http://new-brunswick.net/new-brunswick/whales/pics/orcawhales.jpg&imgrefurl=http://www.new-brunswick.net/new-brunswick/whales/orca.html&h=255&w=350&sz=23&hl=en&start=17&tbnid=c2KGnZrpXTMxJM:&tbnh=87&tbnw=120&prev=/images%3Fq%3Dswimming%2Bwith%2Bkiller%2Bwhales%26gbv%3D2%26svnum%3D10%26hl%3Den%26sa%3DG

Many thanks, TTH, for your great effort.

http://www.sheppardsoftware.com/

Many thanks, Contrex.

Best wishes