Which sentence below is a compound sentence?
a. when the train arrives and if ms. langlois is on it, she will be served with a subpoena.
c. the football game was cancelled because it was raining.
b. unless my girlfriend postpones her visit from calgary, i will not have time to study for my exam.
d. ottawa is the capital of canada, but toronto is the capital of ontario.

The second option (B) is going to be your answer :)

The second option (B) is going to be your answer :)

glamis thou art, and cawdor; and shalt be what thou art promis'd; yet do i fear thy nature; it is too full o' the milk of human kindness to catch the nearest way: thou wouldst be great; art not without ambition; but without the illness should attend it. what thou wouldst highly, that wouldst thou holily; wouldst not play false, and yet wouldst wrongly win: thou'dst have, great glamis, that which cries, "thus thou must do, if thou have it: and that which rather thou dost fear to do than wishest should be undone." hie thee hither, that i may pour my spirits in thine ear; and chastise with the valor of my tongue all that impedes thee from the golden round, which fate and metaphysical aid doth seem to have thee crown'd withal.  

he lacks ambition.  

he is hesitant.  

he lacks courage.  

he has moral scruples.

sentence lenght varies according to word choice.you select which word to use and that will require to use other expressions that collocate with the word chosen.sentence length will vary   according to the choice of words you make to express your ideas.