In considering the materials selection for the upper wing skins of commercial airplanes, which of the the following statements and properties relate to 7xxx (Al-Zn) based alloys and which relate to multi-ply polymer matrix composites.

1. Compared to the material currently used for most airplanes built in the last 20 years this material is capable of achieving a better performance for the three main properties key to the current design (specific strength, specific toughness and SCC resistance)
2. Material with strongly direction dependent properties
3. Material neeeds to be artificially aged at about 150 - 170 degrees Celsius
4. Material that retains sufficient strength up to 600 degrees C
5. Material not susceptible to SCC

A. Polymer matrix composite

B. not applicable to either PMC or 7xxx

C. 7xxx alloy