In a controlled scientific experiment,
a.
no variables are kept constant.
b.
one or more variables are kept constant.
c.
only one variable can be kept constant.
d.
all variables are kept constant.

B one or more variables are kept constant.

Explanation:

one or more variables are kept constant. In a controlled scientific experiment, a scientist alters one variable, called the independent variable. The scientist then studies the effects of this alteration on another variable, called the dependent variable.

lysosomes contain a variety of enzymes, enabling the cell to break down various biomolecules it engulfs, including peptides, nucleic acids, carbohydrates, and lipids (lysosomal lipase). the enzymes responsible for this hydrolysis require an acidic environment for optimal activity. hope i !

the second type of galaxy is called a barred spiral, which has a thing called a bar straddling the nucleus