**Core Concept**
The question tests the student's understanding of the pharmacokinetics of theophylline, particularly the concept of steady-state concentration and the time it takes to reach this state. The key principle involved is the relationship between the rate of drug administration and the time it takes to achieve steady state.

**Why the Correct Answer is Right**
To solve this problem, we use the formula for the time it takes to reach a certain percentage of steady state: t = (ln(%/100) / (1 - %/100)) * (Vd/CL) * ln(2). Plugging in the values given, we get t = (ln(93.75/100) / (1 - 93.75/100)) * (35 L / 48 ml/min) * ln(2). This simplifies to t ≈ 4 hours.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because it is a fixed time interval (e.g., 6 hours) and does not take into account the specific parameters of theophylline's pharmacokinetics.

**Option C:** This option is incorrect because it is a percentage of the maximum dose (e.g., 75% of 250 mg) and does not relate to the concept of steady-state concentration.

**Option D:** This option is incorrect because it is a random number (e.g., 12 hours) and does not have any basis in the pharmacokinetics of theophylline.

**Clinical Pearl / High-Yield Fact**
When administering intravenous infusions, it's essential to consider the pharmacokinetic parameters of the drug to ensure that the patient reaches the desired steady-state concentration in a timely manner. This can be particularly important in emergency situations, such as severe asthma attacks.

**Correct Answer:** C. 4 hours.