Question

which word is a synonym for the word grave? mrs. roberts had grave doubts about letting leticia and megan work together on their assignment since they often argued. several serious hopeful productive

Explanation:

In the given sentence, "grave" describes the nature of Mrs. Roberts' doubts, meaning the doubts are significant and weighty. "Serious" matches this meaning, while the other options do not align with the context of significant doubts.

Answer:

serious