yes similar explanation as scthakur
rem the post which related the nurses' protest to their being overworked. Though another option was available w/t being but still this was the best ans. I have made out that apart from looking at the rules, we shld also pay attention to the meaning of the sentence. I dnt know abt others, but I used 2 do this mistake earlier. I simply looked at rules at selected the ans with correct rule ignoring the meaning of the sentence. (and had 2 pay price for this. Got 640 in GMAt though was quant score was 49, verbal payed havoc

)
so alw read the sentence carefully first , understand its meaning and then go for rules and all.