**Core Concept**
Lente insulin is a type of intermediate-acting insulin that contains a mixture of crystalline and amorphous insulin. The amorphous form of insulin is absorbed more slowly and has a longer duration of action, which helps to regulate blood glucose levels over a longer period.

**Why the Correct Answer is Right**
The correct answer, 30%, indicates that 30% of Lente insulin is in its amorphous form. This amorphous form is absorbed more slowly due to its larger molecular size and the absence of crystal structure. As a result, it has a longer duration of action, typically lasting around 14-18 hours. This slower absorption rate helps to provide a more sustained effect on blood glucose levels.

**Why Each Wrong Option is Incorrect**
**Option A:** 70% is incorrect because the amorphous form of Lente insulin is not as prevalent as the crystalline form, which is responsible for the rapid onset of action.

**Option C:** 50% is incorrect because the exact percentage of amorphous insulin in Lente insulin is lower, at around 30%.

**Option D:** 90% is incorrect because the crystalline form of insulin, which is responsible for the rapid onset of action, is not present in such a high concentration in Lente insulin.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the type and percentage of amorphous insulin in intermediate-acting insulins like Lente can affect the duration and onset of action, which in turn can impact blood glucose control. This highlights the importance of understanding the pharmacokinetic properties of different insulin types.

**✓ Correct Answer: B. 30%**