This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
Which of the following is a long acting insulin that never attains a peak concentration in plasma? 
Select and explain. 
A. Insulin lispro, B. Insulin aspart, C. Insulin glulisine, D. Insulin glargine
D: Insulin glargine
Answer: D: Insulin glargine 
Explanation: (Ref: Katzung 14th ed. P 755)Insulin glargine is a soluble, "peakless" (i.e. having broad concentration plateau), long acting insulin analogue.Onset: 1-1.5 hours. Duration of action: 11-24 hours.Summary of bioavailability characteristics of the insulinsInsulin preparationsOnset of actionPeak actionEffective durationInsulins lispro, aspart, glulisine5-15 minutes1-1.5 hours3-4 hoursHuman regular30-60 minutes2 hours6-8 hoursTechnosphere inhaled insulin5-15 minutes1 hour3 hoursHuman NPH2-4 hoursFlat 24 hoursInsulin detemir0.5-1 hoursFlat17 hoursInsulin degludec0.5-1.5 hoursFlat>42 hours