The practical limit of moisture content achieved in air drying of timber is A. 5% B. 15% C. 25% D. 35%

Option A (5%) is incorrect because timber with a moisture content of 5% is too dry and will be susceptible to cracking and splitting. Option C (25%) is incorrect because timber with a moisture content of 25% is still susceptible to decay and fungal attack. Option D (35%) is incorrect because timber with a moisture content of 35% is too wet and will not be dimensionally stable.