Through which microscope were cells first observed

How many variables are altered in a good experiment? a.1 b.0 c.2 d.3

How does pregnancy begin? a) a placenta forms in the uterus b) a sperm reaches an egg in the fallopian tubec) the blastocyst differentiates into two cell types d) contractions begin in the uterine wallapex

Based on the data in your tables, did the light-colored moths have a higher or lower survival rate after the industrial revolution?