Of secondhand smoke can be harmful.
a. even low levels
b. only high levels
c. neither of the above
d. both a and b

Well really, it could not be both A and B, as option B contains the world 'Only' which means it can not (depending on the context) be put with other options, so that rules D out, low levels of second hand smoke can still be harmful, it is even listed on the National Cancer Institute 

Ithink it is the last one sorry if i’m wrong

Only ten amendments were ratified by the states.