Which of the following best illustrates a pair of sentences that are joined by an understood relationship?
a. luke put three dollars into the office football pool. he was looking forward to vacation.
b. it rained for ten days and ten nights. grandmother grady called a company to drill a well.
c. i don't understand a word you said. have you taken a course in english literature?
(d.) detective smiley scanned the dim hallway. he pulled his pistol from its holster.

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.

the simple predicate of the sentence is camped.