Step 1: Passive to active.
Passive: "The environment has to be saved by people."
Active: Subject (People) + verb (have to save) + object (the environment).
Step 2: Checking options.
(A) Wrong — still passive.
(B) Correct — "People have to save the environment."
(C) Wrong — awkward and incorrect.
(D) Wrong — modal "can" changes meaning.
Step 3: Conclusion.
Correct answer is (B) People have to save the environment.