What's the difference between simple present and present progressive?

[mehran]

Test No. incompl/inter-84 "Simple Present (1)", question 2

But then there are those who are never happy unless they have a problem to ..........

(a) dissolve
(b) solve
(c) cut
(d) release

Test No. incompl/inter-84 "Simple Present (1)", answer 2

But then there are those who are never happy unless they have a problem to solve.

Correct answer: (b) solve
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I have some problem about these will you please send for me some sample test for me about Simple present and Presenet progressive I need to practice. my e-mail address is mehran254@hotmail.com

[Torsten]

Hi,

Please take a look at these lessons:
http://www.english-test.net/lessons/index.html
http://www.english-test.net/lessons/2/index.html

TOEIC listening, photographs: At the optician's