Passive voice is formed using a form of the verb "to be" + past participle of the main verb.
The subject of the passive sentence is the recipient of the action.
Let's analyze the options:
Option
(1) "My parents regard as an ideal couple.
" - This sentence is grammatically awkward as written.
If it meant "My parents regard [them] as an ideal couple," it's active voice (subject "My parents" performs the action "regard").
If it meant "[They] are regarded by my parents as an ideal couple," it would be passive.
As written, it's active but incomplete.
Option
(2) "I asked him to go.
" - Active voice.
Subject "I" performs the action "asked.
"
Option
(3) "Problems have to be confronted.
" - Passive voice.
- "to be confronted" consists of "to be" + past participle "confronted".
- The subject "Problems" is the recipient of the action of confronting.
The agent doing the confronting is not specified (or implied as "by us" or "by people").
- The active equivalent would be something like "We/People have to confront problems.
"
Option
(4) "The tree was striking by lightning.
" - This should be "The tree was struck by lightning" to be grammatically correct passive voice.
"was struck" is "be" (past tense) + past participle "struck".
If corrected, it would be passive.
As written "was striking", it's active past continuous (if it made sense, e.
g.
, "The tree was striking a pose").
Considering the options as given, option (3) is a clear and grammatically correct sentence in the passive voice.