In tenis does your knees have to be slightly flexed for both the forehand and backhand?

Both independent and dependent clauses

In a particular chemical reaction, the energy of the reactants is 30 kj and the energy of the products is 5 kj. 
 the maximum energy of the system is 40 kj. sketch a potential energy diagram for this reaction. make sure to label the energy of the reactants, the energy of the products, the activation energy, and the enthalpy change for the reaction.

Can any one me on number 4? i do know that it’s not a cause i gotten that wrong on the first try.