CAE - English in use 3

Read the text below and look carefully at each line. Some of the lines are correct, and some have a word which should not be there. If a line has a word which should not be there, mark it. In times of trouble when snails have the perfect escape
but retreating into a shell does not always guarantee
a survival. For the land snail, Arianta arbustorum,
faced with local climatic warming in the Swiss city
of Basle, having had a shell has not helped a bit.
Between 1903 and 1991 this snail became really extinct
at 16 out 29 localities around the city. All eight
populations were killed off by urban development but
the other eight sites continue on to support healthy
populations of these other mollusc species. Snail
experts at Basle University checked on the differences
between the sites where the snails all live and those from
which they had been disappeared. The only difference
was ground temperature. Built-up districts which emit
more heat, and in otherwise perfectly suitable habitats
Arianta had died out at sites that were quite artificially
warmer. The difference was often just a few warm degrees.
Small as this very difference was, its effect was huge.