As a result of medical advances, many people that might at one time have died as children of such infections as diphtheria, pneumonia, or rheumatic fever now live well into old age.

(B) who might once have died in childhood

(D) who in childhood might have at one time died

I came down to these two choices. On the one hand, B is better than D because it's more concise. On the other hand, D has "died" immediately followed by "of" and B doesn't. In other words, each has its own reason to be the right one. How would you pick?

Thanks,

J