At what position if the earth in its orbit is it summertime in the northern hemisphere?

position 1
position 2
position 3
position 4

i think it is position 1 but idk

d. sodium chloride ions.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products