16) Jane got wet because she forgot her umbrella. (so)
Jane forgot her umbrella, so she got wet.
17) You should study harder on your examination. (I suggest that)
I suggest that you study harder on your examination.
18) You must learn very hard so that you can pass the exam. (for)
You must learn very hard for passing the exam.
19) To know English is necessary. (It is)
it is necessary to know English.
20) It is very easy to do this grammar exercise. (To inf...)
To do this grammar exercise is very easy.