The fore limbs has the (humerus, ulna, radius, carpals, metacarpals), and digits. While the hind limbs characteristics are the (femur, patella, fibula, tibia,  tarsals, metatarsals), and digits.
        
                    
             
        
        
        
In geology, a graded bed is one characterized by a systematic change in grain or clast size from one side of the bed to the other. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer onesI just learned about this in our rocks and minerals unit for science, 
 
        
             
        
        
        
Answer:
a. positive; negative
Explanation:
Transcription is the process of forming an RNA molecule from a DNA template molecule. In this process, the strands of DNA separate and one serves as a template for RNA, while the other is inactive. At the end of the transcript, the tapes that have been split back together again.
The transcription process is divided into three steps: initiation, stretching and termination
During the stretching phase, transcription chain elongation occurs. In this phase the enzyme called RNA polymerase starts to move through the DNA molecule, unwinding its helix and producing an increasingly lengthened RNA molecule. The already transcribed DNA is rewound almost immediately, recomposing its double helix. This process is called the elongation phase.
During this process, it is believed that positive supercoils  are generated ahead of the transcription bubble and  and the negative supercoils behind it.
 
        
             
        
        
        
Answer:
They have  helical thickening of lignin in their walls to prevent collapse
Explanation:
the primary function of Xylem and its conducting vessels tracheids is to provide  support and tranport  water and  minerals  in plants.
 Xylem vessels  have layers of dead materials in the walls called LIGNIN.   Lignin is a polymer; a  very strong, hard materials that stop water passage  through it,because it contains dead cells, 
Therefore  the presence of  deposit of these strong  impermeable, ligified  walls  in its  walls  prevent its collapse during mass flow of water of transpiration pull.