17. В каком предложении употреблена краткая форма прилагательного?
А) В поле дышится спокойно.
B) Море спокойно.
C) Ребёнок спит спокойно.
D) Кругом тихо и спокойно.
E) Говорить надо спокойно.​

The answer is letter A.

the present continuous is a verb tense which is mainly used to indicates that an action is in progress at the moment of speaking.  

it is formed using: person + verb to be (am/is/are) +verb + - ing form  

example: i am studying at this moment .

in addition, the present continuous is also used in order to express things that will or will not happen in the near future.

example: i am having dinner with some friends tonight.

the speaker sometimes   uses it   to express that an action is repeated and it causes irritation on the part of the speaker

example: my sister is constantly complaining about everything.