Excerpt from quilts and rugs
kate mcconnaughey

(10) some of the heirloom quilts which still exist are marvels of design and stitching.
read the passage. look at the underlined section marked number 10. there may be a mistake in the way the sentence is written. if you find a mistake, choose the answer that corrects the mistake. if there is no mistake, choose ‘correct as is.’
a) correct as is.
b) some of the heirloom quilts are marvels of design and stitching which still exist.
c) some of the heirloom quilts are marvels which still exist of design and stitching.
d) which still exist, some of the heirloom quilts which still exist are marvels of design and stitching.

the two answers are

get thee back into the tempest and the night's plutonian shore

on the pallid bust of pallas just above my chamber door

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.