Step 1: Analyze the given 3D hollow geometry (Figure D). It consists of six triangular faces and nine equal edges, forming a symmetrical structure.
Step 2: Identify which given net diagrams (P, Q, R, S) can be folded along the dotted lines to form the described 3D shape.
- Option P: Contains six triangles arranged in a way that they can be folded into a symmetrical 3D figure.
- Option Q: Also consists of six triangles correctly placed for forming the shape.
- Option R: Maintains the same triangular face count and edge arrangement, making it valid.
- Option S: The triangular faces are not arranged correctly to form the required 3D structure.
Step 3: Since P, Q, and R can be folded into the required 3D shape, the correct answer is:
\[ \text{P, Q, and R} \] Thus, the correct answer is option C.
Let $ a_0, a_1, ..., a_{23} $ be real numbers such that $$ \left(1 + \frac{2}{5}x \right)^{23} = \sum_{i=0}^{23} a_i x^i $$ for every real number $ x $. Let $ a_r $ be the largest among the numbers $ a_j $ for $ 0 \leq j \leq 23 $. Then the value of $ r $ is ________.
A temperature difference can generate e.m.f. in some materials. Let $ S $ be the e.m.f. produced per unit temperature difference between the ends of a wire, $ \sigma $ the electrical conductivity and $ \kappa $ the thermal conductivity of the material of the wire. Taking $ M, L, T, I $ and $ K $ as dimensions of mass, length, time, current and temperature, respectively, the dimensional formula of the quantity $ Z = \frac{S^2 \sigma}{\kappa} $ is: