( )___ you go mountain hiking , you should bring water with you.(1)Whoever (2)Whatever (3)Whenever (4)However?

Not whatever, whoever due to pronoun you as object being spoken to already;
(3)whenever=subordinate clause of time to main clause:-
(--)Whenever you go mountain hiking;-------subordinate clause
you should bring water with you.-----main clause10marks.

應該選表示[時間點]的關係副詞whenever來帶出副詞子句當修飾語,因為這句的附屬子句與主要子句的關係是建立在時間上.

whatever, whoever是[關係代名詞]不能用在本附屬子句,因為子句有了自己主詞you
however雖可當連接副詞用,但本句的句意不是兩個相反的狀況,不能用however

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