1。Although good health depends on a number of factors, in general there is a close correlation between the wealth of a country as well as the health status of its people .
good health
a number of
as well as
its people

2。Marine snails are occurred in all seas from the Arctic to the Antarctic, though they reach their greatest development in tropical waters.
are occurred
all seas
though
greatest

3。That people consider a luxury at one time frequently becomes a necessity ; many families find that ownership of two cars is indispensible.

That
a luxury
frequently
that ownership