—How was your day, Linda?—________________
Maria has _____ trouble _____ math, so she often asks her math teacher for help.
The rivers in Changshun are clearer than _____ in Wuhan..
—Does your father still smoke?—No, he has succeeded in_____ smoking for three years.
I think that you have made rapid _____ in math.
I find _______necessary to do everything we can ____________protect the environment.