estion 19: A robot vacuum cleaner is a
. help
B. helpless
estion 20: It is convenient for you to read
. e-books
B. laptops
estion 21: Most smartphones now
. display
B. offer
stion 22: We can surf the
. e-book
estion 23: You can get access
puters, mobile phones, and tablets.
B. in
. for ...
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