The numerous illnesses and injuries suffered by John F. Kennedy during his presidency
have been relatively well established by recently released records, but what is much more challenging to determine are the effect of his health problems on his presidential decisions, on his family life, and on his legacy.
A. have been relatively well established by recently released records, but what is much more challenging to determine are
B. has been relatively well established by recently released records, but what is much more challenging to determine is
C. have been relatively well established by recently released records, but what is much more challenging to determine is
D. has been relatively well established by recently released records, but what is much more challenging to determine are
E. is relatively well established by recently released records, but that which is much more challenging to determine is