What makes a reading text easy or difficult??

generally, reading texts are easier if :
a. they contain 'simple' language-structure and vocabulary familiar to the students
b. they are short : simple sentences
c. they are clearly organized eg. there is a straightforward storyline or a clearly signposted argument
d. they are factual
e. they are in standard english with no specialized vocabulary
f. the topic is concrete and familiar
g. there is support in the way of layout, tittles, pictures, graphs, etc.