Though dentists recommend brushing one’s teeth three times a day

Difference between D and E is the usage of 'And' VS 'But'.

We need to say --Though dentist say brush.. thrice everday..most adults brush twice daily AND hardly floss. But denotes a contrast that is not required here. Hence E.
HTH

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A. brush just twice a day and floss hardly never
hardly never - means almost all the time. hardly ever -> rarely

B. brush your teeth twice and never floss
your does not have an antecedent.

C. brush just twice but rarely floss at all
but introduces a contrast that is not needed.
just twice - twice in a lifetime? twice a week?

D. brush twice daily but hardly ever floss
same error as in C.

E. only brush twice daily and rarely floss at all
only brush correctly states that they only brush
only brush is parallel to rarely floss

i am having trouble understanding this question, can someone shed some more insight. doesn't all other choices apart from A change the meaning of the original sentence, from what i understand the question states dentists recommed brushing thrice but american adults brush twice and floss always(hardly never means eveytime). but all choices says they never floss which is opposite of what is stated in the original sentences.Isn't changing meaning wrong in GMAT?????

Though dentists recommend brushing one’s teeth three times a day, many adult Americans brush just twice a day and floss hardly never.

A. brush just twice a day and floss hardly never The adverb of frequency should go before the verb and "hardly never" is not idiomatic.
B. brush your teeth twice and never floss "Your" is definitely the wrong pronoun.
C. brush just twice but rarely floss at all "a day" or "daily" is missing.
D. brush twice daily but hardly ever floss "but" implies that brushing twice daily is sufficient, and a word to indicate that this is less than the desired three times a day is missing
E. only brush twice daily and rarely floss at all

Though dentists recommend brushing one’s teeth three times a day, many adult Americans brush just twice a day and floss hardly never.

A. brush just twice a day and floss hardly never
"hardly never" should be before floss if anything, but also it sounds quite dumb (hardly never does indeed mean always)

B. brush your teeth twice and never floss
"your" is wrong, they brush their teeth, not mine.

C. brush just twice but rarely floss at all
usage of "but" is unfounded, would make more sense if "but floss very often" but that is not the case

D. brush twice daily but hardly ever floss
again "but" is abit wrong, coz the first part and second part are both "weak". Would make more sensee if they "brush 4 times daily but hardly ever floss"

E. only brush twice daily and rarely floss at all
perfect

If option A had ended "floss hardly ever" could it have been correct? Asking for a friend who may or may not have totally misread the question :P

I choose E. only brush twice daily and rarely floss at all. I brush my teeth twice a day and sometimes use floss. It’s enough for me. I don’t have any problems or diseases, so I don’t need any special treatment. For me it’s just important to use a good toothpaste and a toothbrush of a good quality. I purchase them at https://mental-dental.com/. It helps me to maintain my teeth white and healthy. And also cleaning every half year is essential.

B is definitely wrong, as it changes the meaning to ‘many Adult Americans brush the reader’s teeth’.

A should also be out, ‘floss hardly never’ is very awkward and the proper phrase is ‘hardly ever’.

C changes the meaning again, this time to mean that many adult Americans only brush twice, ever.

D also has a very slight meaning change, by removing the word ‘just’ it weakens the implication that brushing twice a day is not enough.

E preserves the meaning the best (it uses ‘only’ in place of ‘just’) and is the clearest

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