Read the text below and choose the correct word for each space. For each question, circle letter A, B, C or D next to the answer you choose.

Dolphins communicate mainly by (46)________ of sounds. These sounds not only (47)________ whistles, but also so-called pulsed sounds, which are often described as squawks, barks, rasps, etc. However, they also use breaching (jumping and falling back into the (48)________ with a loud splash) and pectoral fin (or flipper) and tail (or fluke) slaps (hitting the flipper or fluke on the water surface). Body posturing and jaw popping also have a role in (49)________. As for language, we do not know (50)________ they have one. Several studies have demonstrated that dolphins can understand a structured language like (51)________. This has been demonstrated for a number of other animal species as well (gorilla, California sea lion, and parrot). Some studies also indicate that dolphin vocalizations are complex (52)________ to support some form of language. (53)________, it has not been demonstrated (54)________ that they can undoubtedly communicate (55)________ themselves.

Dolphins communicate mainly by (46)________ of sounds.