endocrinology Q2

a 70 years old man is admitted in a confused state.on examination he is apyrexial and ther is no focal neurological signs.HR 75 bpm, Bp 130/90 without postural drop.the chest is clear and abdomen is unremarkable.these are the blood findings:
Hb 13.5
WBC 5.5
plt 220

Na 108
K 4.5
urea 10
creatinie 80
glucose 4.5

bili 8
AST 20
ALT 21
ALP 65

what is the most likely cause?
1-diabetes insipidus
2-psuedo-hyponatraemia
3-SIADH
4-addison's disease
5-water intoxication

what investigation should be organised next?
1-water deprivation
2-short synachtin test
3-paired urine and serum osmolalties
4-CXR
5-CT head