The uterine lining, or endometrium, is the internal layer of the uterus which thickens and gets filled with blood vessels in preparation to receive a fertilized egg. If this does not happen, the uterus removes this extra layer through the vagina, in a process called menstrual flow, which lasts 5 days average.
        
             
        
        
        
Answer: 4
Explanation:
It is composed of a cell, but does not have
tissues.
 
        
                    
             
        
        
        
Answer:
Constant variables
Explanation:
Elaina's investigation lacked the critical ingredient of constant variables which are important components of every scientific investigation. In every research, there are 3 important variables, namely:
1. Dependent variables: the actual variable to be measured during the course of investigations and whose values are dependent on another variable (independent variable) supplied by the investigators.
2. Independent variable: one of the variables that are supplied by investigators whose values are often manipulated to see the kind of changes it will cause to the dependent variable. 
3. Constant variables: other variables that are neither independent nor dependent but constant for all the various experimental groups in investigations. 
 
        
             
        
        
        
It’s called a solar system because solar means “relating to or determined by the sun” and system means “a set of things working together as parts of a mechanism or an interconnecting network” and the solar system is a whole bunch of planets and other things that are related to the sun and working together.
        
             
        
        
        
Hi! glycolipids and glycoproteins are important Because it helps to stabilise membrane structure.