If a2 + b2 + c2 = 281 and ab + bc + ca =4, then a + b + c is  Choose the correct choice from the following:  A) 16  B) 18  C) 22  D) 17  E) 20

Rationale: "by formula , ( a + b + c ) ^ 2 = a ^ 2 + b ^ 2 + c ^ 2 + 2 ( ab + bc + ca ) , since , a ^ 2 + b ^ 2 + c ^ 2 = 281 and ab + bc + ca = 4 , ( a + b + c ) ^ 2 = 281 + 2 ( 4 ) = 289 = 17 ^ 2 therefore : a + b + c = 17 answer : d"
Answer: D