At the gastrula stage, students should make a new model that now contains three colors of clay (to represent the three germ layers).
(students; should make; a new model that now contains three colors of clay (to represent the three germ layers); T:At the gastrula stage) (a new model; contains; three colors of clay; T:now)
students a new model
should make contains
a new model that now contains three colors of clay (to represent the three germ layers) T:At the gastrula stage
three colors of clay T:now