The correct option is B magazines
The suitable word must be plural, as suggested by the words 'are'
and 'many'. The verb 'are' is a plural verb ('is' is singular). When the
verb is plural, the noun in relation must also be plural. 'Many' refers
to a plural noun.
Option B: 'Magazines' is a plural noun and completes the sentence in meaning. Hence this option is correct.
Options
A, C and D: 'Paper' and 'book' are singular nouns. 'Dust' is an uncountable noun whereas 'many' only modifies countable nouns.
These words do
not match with the determiner 'many'; 'many' refers to more than one.
Hence these options are incorrect.